U.S. patent number 8,470,254 [Application Number 13/239,898] was granted by the patent office on 2013-06-25 for honeycomb filter and method for producing honeycomb filter.
This patent grant is currently assigned to NGK Insulators, Ltd.. The grantee listed for this patent is Shingo Iwasaki, Yukio Miyairi, Takashi Mizutani. Invention is credited to Shingo Iwasaki, Yukio Miyairi, Takashi Mizutani.
United States Patent |
8,470,254 |
Mizutani , et al. |
June 25, 2013 |
Honeycomb filter and method for producing honeycomb filter
Abstract
There is provided a honeycomb filter wherein particles having an
average particle diameter smaller that of the particles
constituting partition walls are deposited at least in open pores
formed by the particles constituting the partition walls and/or
gaps between the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side, thereby forming a
composite region. The average pore diameter of the partition walls
is 5 to 40 .mu.m, and the porosity of the partition wall is 35 to
75%. The particles to be deposited have an average particle
diameter of 1 to 15 .mu.m, and the height of the composite region
is not more than 80 .mu.m in the direction from the outermost
contour line of the partition walls to the surface of the partition
walls.
Inventors: |
Mizutani; Takashi (Tokoname,
JP), Iwasaki; Shingo (Gifu, JP), Miyairi;
Yukio (Nagoya, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mizutani; Takashi
Iwasaki; Shingo
Miyairi; Yukio |
Tokoname
Gifu
Nagoya |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
NGK Insulators, Ltd. (Nagoya,
JP)
|
Family
ID: |
42780704 |
Appl.
No.: |
13/239,898 |
Filed: |
September 22, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120009092 A1 |
Jan 12, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2010/053149 |
Feb 26, 2010 |
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Foreign Application Priority Data
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Mar 26, 2009 [JP] |
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2009-076142 |
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Current U.S.
Class: |
422/177;
422/180 |
Current CPC
Class: |
C04B
35/565 (20130101); C04B 41/5059 (20130101); C04B
35/573 (20130101); B01J 23/002 (20130101); C04B
41/87 (20130101); C04B 28/24 (20130101); B01J
23/63 (20130101); C04B 35/63416 (20130101); C04B
37/005 (20130101); B01J 37/0215 (20130101); B01J
35/0006 (20130101); B01J 35/023 (20130101); C04B
38/0019 (20130101); C04B 38/0009 (20130101); B01J
35/04 (20130101); C04B 41/009 (20130101); C04B
38/0009 (20130101); C04B 35/565 (20130101); C04B
38/0054 (20130101); C04B 38/0074 (20130101); C04B
28/24 (20130101); C04B 14/324 (20130101); C04B
14/4656 (20130101); C04B 16/0641 (20130101); C04B
38/0019 (20130101); C04B 41/009 (20130101); C04B
35/00 (20130101); C04B 38/0006 (20130101); C04B
41/009 (20130101); C04B 35/565 (20130101); C04B
38/0006 (20130101); C04B 41/5059 (20130101); C04B
41/0072 (20130101); C04B 41/4515 (20130101); C04B
41/4547 (20130101); C04B 41/457 (20130101); C04B
2237/704 (20130101); C04B 2235/5472 (20130101); C04B
2235/5436 (20130101); F01N 3/0222 (20130101); C04B
2235/6567 (20130101); C04B 2235/3826 (20130101); C04B
2235/6583 (20130101); F01N 2330/60 (20130101); C04B
2235/656 (20130101); C04B 2237/09 (20130101); C04B
2235/528 (20130101); B01J 2523/00 (20130101); C04B
2237/083 (20130101); C04B 2235/428 (20130101); C04B
2237/62 (20130101); C04B 2235/5228 (20130101); C04B
2237/365 (20130101); C04B 2111/0081 (20130101); C04B
2111/00793 (20130101); B01J 2523/00 (20130101); B01J
2523/36 (20130101); B01J 2523/3712 (20130101); B01J
2523/3718 (20130101); B01J 2523/48 (20130101); B01J
2523/72 (20130101) |
Current International
Class: |
B01D
50/00 (20060101) |
Field of
Search: |
;422/177,180 ;428/116
;502/423 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 174 698 |
|
Apr 2010 |
|
EP |
|
63-240912 |
|
Jun 1988 |
|
JP |
|
2002-519186 |
|
Jul 2002 |
|
JP |
|
2004-340023 |
|
Dec 2004 |
|
JP |
|
2006-007117 |
|
Jan 2006 |
|
JP |
|
2607898 |
|
Nov 2006 |
|
JP |
|
2010-29848 |
|
Feb 2010 |
|
JP |
|
2010-111567 |
|
May 2010 |
|
JP |
|
2006-041174 |
|
Apr 2006 |
|
WO |
|
2008/066167 |
|
Jun 2008 |
|
WO |
|
Primary Examiner: Duong; Tom
Attorney, Agent or Firm: Burr & Brown
Claims
The invention claimed is:
1. A honeycomb filter comprising a honeycomb-structured substrate
provided with a plurality of cells separated by partition walls of
porous ceramic having pores and functioning as exhaust gas
passages, the honeycomb-structured substrate having an exhaust gas
inflow side and an exhaust gas outflow side, wherein plugging
portions are formed alternately in one side open end portions and
the other side open end portions of the plural cells, at least in
open pores formed by the particles constituting the partition walls
and/or gaps between the particles, a composite region is formed by
depositing particles having an average particle diameter smaller
than that of the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side, the partition walls
have an average pore diameter of 5 to 40 .mu.m and a porosity of 35
to 75%, the particles deposited have an average particle diameter
of 1 to 15 .mu.m, and the composite region has a height of 80 .mu.m
or less with respect to the partition wall surface direction from
the outermost contour line of the partition walls.
2. The honeycomb filter according to claim 1, wherein the particles
having an average particle diameter smaller than the average size
of the open pores formed by the particles constituting the
partition walls and/or gaps between the particles are deposited to
form the composite region.
3. The honeycomb filter according to claim 1, wherein the composite
region is formed in the open pores and/or the gaps between the
particles in the range from a surface layer reference line of the
partition walls on the exhaust gas inflow side to a position of 30%
of the partition wall thickness.
4. The honeycomb filter according to claim 1, wherein the composite
region is formed in the open pores and/or the gaps between the
particles in the range from a surface layer reference line of the
partition wall on the exhaust gas inflow side to a position of the
depth of at most 4 times the average pore diameter of the partition
walls.
5. The honeycomb filter according to claim 1, wherein the particles
deposited in the open pores and/or the gaps between the particles
are formed of the same material as that for the particles
constituting the partition walls.
6. The honeycomb filter according to claim 1, wherein the particles
constituting the partition walls are formed of silicon carbide or a
composite material of silicon carbide and silicon.
7. The honeycomb filter according to claim 1, wherein the particles
deposited in the open pores and/or the gaps between the particles
are bonded by a bonding phase different from the framework
particles constituting the partition walls.
8. The honeycomb filter according to claim 1, wherein the particles
deposited in the open pores and/or the gaps between the particles
are bonded by a silica phase.
9. The honeycomb filter according to claim 1, wherein a catalyst is
loaded on a part of or the entire portion of the partition walls
and/or a part of or the entire portion of the composite region.
10. The honeycomb filter according to claim 1, wherein the
composite region has a height of at least 5 .mu.m to 80 .mu.m or
less with respect to the partition wall surface direction from the
outermost contour line of the partition wall.
11. A method for producing a honeycomb filter, the method
comprising: forming a honeycomb formed body by subjecting a forming
raw material containing a ceramic raw material to extrusion forming
and forming plugging portions alternately in one side open end
portions and the other side open end portions of the plural cells
of the honeycomb formed body, firing the honeycomb formed body to
form a honeycomb fired body, supplying particles having an average
particle diameter smaller than that of the particles constituting
the partition walls from the one side open end portions of the
honeycomb fired body by a solid-gas two-phase flow, and at least in
open pores formed by the particles constituting the partition walls
and/or gaps between the particles, forming a composite region by
depositing particles having an average particle diameter smaller
than that of the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side; wherein the
partition walls have an average pore diameter of 5 to 40 .mu.m and
a porosity of 35 to 75%, the particles deposited have an average
particle diameter of 1 to 15 .mu.m, and the composite region has a
height of 80 .mu.m or less with respect to the partition wall
surface direction from the outermost contour line of the partition
walls.
12. The method for producing a honeycomb filter according to claim
11, wherein the method comprises: supplying particles having an
average particle diameter smaller than that of the particles
constituting the partition walls from one side open end portion of
the honeycomb fired body, and simultaneously, sucking the particles
from the other open end portions of the honeycomb fired article to
deposit the particles in the pores formed in the partition walls on
the exhaust gas inflow side to form a composite region.
13. A method for producing a honeycomb filter, the method
comprising: forming a honeycomb formed body by subjecting a forming
raw material containing a ceramic raw material to extrusion forming
and forming plugging portions alternately in one side open end
portions and the other side open end portions of the plural cells
of the honeycomb formed body, firing the honeycomb formed body to
form a honeycomb fired body, supplying particles having an average
particle diameter smaller than that of the particles constituting
the partition walls from the one side open end portions of the
honeycomb fired body by a solid-gas two-phase flow, at least in
open pores formed by the particles constituting the partition walls
and/or gaps between the particles, forming a composite region by
depositing particles having an average particle diameter smaller
than that of the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side, and further
performing a thermal treatment; wherein the partition walls have an
average pore diameter of 5 to 40 .mu.m and a porosity of 35 to 75%,
the particles deposited have an average particle diameter of 1 to
15 .mu.m, and the composite region has a height of 80 .mu.m or less
with respect to the partition wall surface direction from the
outermost contour line of the partition walls.
14. The method for producing a honeycomb filter according to claim
13, wherein the method comprises: supplying particles having an
average particle diameter smaller than that of the particles
constituting the partition walls from one side open end portion of
the honeycomb fired body, and simultaneously, sucking the particles
from the other open end portions of the honeycomb fired article to
deposit the particles in the pores formed in the partition walls on
the exhaust gas inflow side to form a composite region.
15. A method for producing a honeycomb filter, the method
comprising: forming a honeycomb formed body by subjecting a forming
raw material containing a ceramic raw material to extrusion forming
and forming plugging portions alternately in one side open end
portions and the other side open end portions of the plural cells
of the honeycomb formed body, firing the honeycomb formed body to
form a honeycomb fired body, loading a catalyst on the partition
walls of the honeycomb fired body to obtain a catalyst-loaded
honeycomb-structured body, supplying particles having an average
particle diameter smaller than that of the particles constituting
the partition walls from the one side open end portions of the
honeycomb-structured body with the catalyst by a solid-gas
two-phase flow, at least in open pores formed by the particles
constituting the partition walls and/or gaps between the particles,
forming a composite region by depositing particles having an
average particle diameter smaller than that of the particles in a
surface layer portion of the partition walls on the exhaust gas
inflow side, and further performing a thermal treatment; wherein
the partition walls have an average pore diameter of 5 to 40 .mu.m
and a porosity of 35 to 75%, the particles deposited have an
average particle diameter of 1 to 15 .mu.m, and the composite
region has a height of 80 .mu.m or less with respect to the
partition wall surface direction from the outermost contour line of
the partition walls.
16. The method for producing a honeycomb filter according to claim
15, wherein the method comprises: supplying particles having an
average particle diameter smaller than that of the particles
constituting the partition walls from one side open end portion of
the honeycomb fired body, and simultaneously, sucking the particles
from the other open end portions of the honeycomb fired article to
deposit the particles in the pores formed in the partition walls on
the exhaust gas inflow side to form a composite region.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a honeycomb filter used for
trapping or cleaning up particulates contained in exhaust gas
discharged from an internal combustion engine such as a diesel
engine or various combustion apparatuses and to a method for
producing the honeycomb filter.
2. Description of Related Art
A large mount of particulate matter (hereinbelow referred to as
"particulate matter", "particulates", or "PM") anchored by soot
(graphite) is contained in exhaust gas discharged from an internal
combustion engine such as a diesel engine or various combustion
apparatuses (hereinbelow appropriately referred to as "internal
combustion engine and the like"). Since environmental pollution is
caused when the particulates are released without change into the
atmosphere, it is general that a filter for trapping particulates
is mounted in the exhaust gas passage from the internal combustion
engine or the like.
An example of the filter used for such a purpose is a honeycomb
filter having a honeycomb-structured body having a plurality of
cells separated by partition walls formed of porous ceramic having
a large number of pores and functioning as exhaust gas passages
with one side open end portions and the other side open end port
ions of plural cells being alternately plugged with plugging
portions. In such a honeycomb filter, when exhaust gas is sent into
the exhaust gas inflow cells (cells not plugged on the exhaust gas
inflow side), particulates in the exhaust gas are trapped when
exhaust gas passes through the partition walls, and purified gas
from which the particulates are removed is discharged from the
purified gas outflow cells (cells not plugged on the exhaust gas
outflow side).
However, in such a conventional honeycomb filter, there arises a
problem of easily causing pressure loss in the partition walls in
accordance with a deposition mode of soot or ash. In particular, in
order to reduce pressure loss to improve the trapping efficiency,
it is effective to impart properties of pores having a small
average pore diameter to a honeycomb filter. However, when a layer
having such properties is formed on the partition walls of the
honeycomb filter, pressure loss of the partition walls is increased
when the exhaust gas passes through the partition walls at high
flow rates. Therefore, in a conventional honeycomb filter, it is
difficult to realize improvement in purification performance and
regeneration efficiency simultaneously with planning the reduction
of pressure loss.
For the aforementioned problems, there are the following Patent
Documents 1 and 2.
The Patent Document 1 discloses a ceramic filter "provided with a
fine particle portion having an average pore diameter of 1 to 10
.mu.m and a thickness of at least 10 times the average pore
diameter on a surface on one side of a support layer formed of a
ceramic filter porous body" for the purpose of providing "a ceramic
filter for exhaust gas, the filter having little change of pressure
loss with the passage of time after trapping and high trapping
efficiency and being excellent on practical side.
The Patent Document 2 discloses a "surface filter for fine
particles, the filter having passages selectively clogged and a
micro porous membrane imparted to the surfaces of the passages,
being formed of a porous honeycomb monolith structure, and being
regenerable by reverse flushing" for the purpose of providing "a
new filtering apparatus regenerable by a reverse flushing
treatment".
However, the Patent Documents 1 and 2 aim to improve PM-trapping
performance by forming a layer having an average pore diameter
smaller than that of the partition walls on the partition walls. In
such a case, the opening of the cell on the exhaust gas inflow side
as an inlet channel becomes small for the thickness of the layer
formed therein. Therefore, there arises a problem of remarkable
increase in the pressure loss of the partition walls particularly
when the exhaust gas passes through the partition walls at high
flow rates. On the other hand, reduction of the thickness of the
partition wall can be considered for avoiding the problem. However,
since thermal capacity is reduced when the thickness of the
partition walls is reduced, and inlet temperature (temperature of
the exhaust gas inflow side end face in the honeycomb filter) may
be varied upon regeneration to become higher than the target
temperature. In such a case, since quick combustion of soot may be
caused to sharply raise the temperature inside the honeycomb
filter, a crack may easily be caused in the honeycomb filter.
As described above, a response to the conventional problems is
still insufficient even by the Patent Documents 1 and 2, and a
solution in the early stages is desired.
PRIOR ART DOCUMENT
Patent Document
Patent Document 1: JP-A-63-240912
Patent Document 2: Japanese Utility Model Registration No.
2607898.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned
prior art problems and aims to provide a honeycomb filter capable
of reducing pressure loss of the partition walls when exhaust gas
passes through the partition walls at high flow rates with
obtaining the same effect as in the layer formed on the partition
walls by forming, at least in open pores formed by the particles
constituting the partition walls and/or gaps between the particles,
a composite region by depositing particles having an average
particle diameter smaller than that of the aforementioned particles
in a surface layer portion of the partition walls on the exhaust
gas inflow side, allowing the partition walls to have an average
pore diameter of 5 to 40 .mu.m and a porosity of 35 to 75%,
allowing the particles deposited to have an average particle
diameter of 1 to 15 .mu.m, and allowing the composite region to
have a height of 80 .mu.m or less with respect to the partition
wall surface direction from the outermost contour line of the
partition walls; and a method for producing the honeycomb filter.
In addition, the present invention aims to provide a honeycomb
filter improving regeneration efficiency with improving
purification performance, a honeycomb filter improving high
trapping efficiency with reducing pressure loss due to the adhesion
of soot, and a honeycomb filter reducing the pressure loss after
ash deposition; and a method for producing the honeycomb
filter.
According to the present invention, there are provided the
following honeycomb filter and method for producing the honeycomb
filter.
According to a first aspect of the present invention, a honeycomb
filter is provided, comprising a honeycomb-structured substrate
provided with a plurality of cells separated by partition walls of
porous ceramic having pores and functioning as exhaust gas
passages, the honeycomb-structured substrate having an exhaust gas
inflow side and an exhaust gas outflow side, wherein plugging
portions are formed alternately in one side open end portions and
the other side open end portions of the plural cells, at least in
open pores formed by the particles constituting the partition wall
and/or gaps between the particles, a composite region is formed by
depositing particles having an average particle diameter smaller
than that of the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side, the partition walls
have an average pore diameter of 5 to 40 .mu.m and a porosity of 35
to 75%, the particles deposited have an average particle diameter
of 1 to 15 .mu.m, and the composite region has a height of 80 .mu.m
or less with respect to the partition wall surface direction from
the outermost contour line of the partition walls.
According to a second aspect, the honeycomb filter according to the
first aspect is provided, wherein the particles having an average
particle diameter smaller than the average size of the open pores
formed by the particles constituting the partition walls and/or
gaps between the particles are deposited to form the composite
region.
According to a third aspect, the honeycomb filter according to the
first or second aspects is provided, wherein the composite region
is formed in the open pores and/or the gaps between the particles
in the range from a surface layer reference line of the partition
wall on the exhaust gas inflow side to a position of 30% of the
partition wall thickness.
According to a fourth aspect, the honeycomb filter according to any
of the first to third aspects is provided, wherein the composite
region is formed in the open pores and/or the gaps between the
particles in the range from a surface layer reference line of the
partition wall on the exhaust gas inflow side to a position of the
depth of at most 4 times the average pore diameter of the partition
walls.
According to a fifth aspect, the honeycomb filter according to any
of the first to fourth aspects is provided, wherein the particles
deposited in the open pores and/or the gaps between the particles
are formed of the same material as that for the particles
constituting the partition walls.
According to a sixth aspect, the honeycomb filter according to any
of the first to fifth aspects is provided, wherein the particles
constituting the partition walls are formed of silicon carbide or a
composite material of silicon carbide and silicon.
According to a seventh aspect, the honeycomb filter according to
any of the first to sixth aspects is provided, wherein the
particles deposited in the open pores and/or the gaps between the
particles are bonded by a bonding phase different from the
framework particles constituting the partition walls.
According to an eighth aspect, the honeycomb filter according to
any of the first to seventh aspects is provided, wherein the
particles deposited in the open pores and/or the gaps between the
particles are bonded by a silica phase.
According to a ninth aspect, the honeycomb filter according to any
of the first to eighth aspects is provided, wherein a catalyst is
loaded on a part of or the entire portion of the partition walls
and/or a part of or the entire portion of the composite region.
According a tenth aspect of the present invention, a method for
producing a honeycomb filter is provided, the method comprising:
forming a honeycomb formed body by subjecting a forming raw
material containing a ceramic raw material to extrusion forming and
forming plugging portions alternately in one side open end portions
and the other side open end portions of the plural cells of the
honeycomb formed body, firing the honeycomb formed body to form a
honeycomb fired body, supplying particles having an average
particle diameter smaller than that of the particles constituting
the partition walls from the one side open end portions of the
honeycomb fired body by a solid-gas two-phase flow, and at least in
open pores formed by the particles constituting the partition walls
and/or gaps between the particles, forming a composite region by
depositing particles having an average particle diameter smaller
than that of the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side; wherein the
partition walls have an average pore diameter of 5 to 40 .mu.m and
a porosity of 35 to 75%, the particles deposited has an average
particle diameter of 1 to 15 .mu.m, and the composite region has a
height of 80 .mu.m or less with respect to the partition wall
surface direction from the outermost contour line of the partition
walls.
According to an eleventh aspect of the present invention, a method
for producing a honeycomb filter is provided, the method
comprising: forming a honeycomb formed body by subjecting a forming
raw material containing a ceramic raw material to extrusion forming
and forming plugging portions alternately in one side open end
portions and the other side open end portions of the plural cells
of the honeycomb formed body, firing the honeycomb formed body to
form a honeycomb fired body, supplying particles having an average
particle diameter smaller than that of the particles constituting
the partition walls from the one side open end portions of the
honeycomb fired body by a solid-gas two-phase flow, at least in
open pores formed by the particles constituting the partition wall
and/or gaps between the particles, forming a composite region by
depositing particles having an average particle diameter smaller
than that of the particles in a surface layer portion of the
partition walls on the exhaust gas inflow side, and further
performing a thermal treatment; wherein the partition walls have an
average pore diameter of 5 to 40 .mu.m and a porosity of 35 to 75%,
the particles deposited has an average particle diameter of 1 to 15
.mu.m, and the composite region has a height of 80 .mu.m or less
with respect to the partition wall surface direction from the
outermost contour line of the partition walls.
According to a twelfth aspect of the present invention, a method
for producing a honeycomb filter is provided, the method
comprising: forming a honeycomb formed body by subjecting a forming
raw material containing a ceramic raw material to extrusion forming
and forming plugging portions alternately in one side open end
portions and the other side open end portions of the plural cells
of the honeycomb formed body, firing the honeycomb formed body to
form a honeycomb fired body, loading a catalyst on the partition
walls of the honeycomb fired body to obtain a catalyst-loaded
honeycomb-structured body, supplying particles having an average
particle diameter smaller than that of the particles constituting
the partition walls from the one side open end portions of the
honeycomb-structured body with the catalyst by a solid-gas
two-phase flow, at least in open pores formed by the particles
constituting the partition walls and/or gaps between the particles,
forming a composite region by depositing particles having an
average particle diameter smaller than that of the particles in a
surface layer portion of the partition walls on the exhaust gas
inflow side, and further performing a thermal treatment; wherein
the partition walls have an average pore diameter of 5 to 40 .mu.m
and a porosity of 35 to 75%, the particles deposited has an average
particle diameter of 1 to 15 .mu.m, and the composite region has a
height of 80 .mu.m or less with respect to the partition wall
surface direction from the outermost contour line of the partition
walls.
According to a thirteenth aspect, the method for producing a
honeycomb filter according to any of the tenth to twelfth aspects
is provided, wherein the method comprises: supplying particles
having an average particle diameter smaller than that of the
particles constituting the partition walls from one side open end
portion of the honeycomb fired body, and simultaneously, sucking
the particles from the other open end portions of the honeycomb
fired body to deposit the particles in the pores formed in the
partition walls on the exhaust gas inflow side to form a composite
region.
According to a honeycomb filter of the present invention, there is
exhibited an excellent effect of being capable of providing a
honeycomb filter capable of reducing pressure loss of the partition
walls when exhaust gas passes through the partition walls with
obtaining the same effect as in the layer formed on the partition
walls by forming, at least in open pores formed by the particles
constituting the partition walls and/or gaps between the particles,
a composite region by depositing particles having an average
particle diameter smaller than that of the aforementioned particles
in a surface layer portion of the partition walls on the exhaust
gas inflow side, allowing the partition walls to have an average
pore diameter of 5 to 40 .mu.m and a porosity of 35 to 75%,
allowing the particles deposited to have an average particle
diameter of 1 to 15 .mu.m, and allowing the composite region to
have a height of 80 .mu.m or less with respect to the partition
wall surface direction from the outermost contour line of the
partition walls; and a method for producing the honeycomb filter.
In addition, there is provided a honeycomb filter improving
regeneration efficiency with improving purification performance, a
honeycomb filter improving high trapping efficiency with reducing
pressure loss due to the adhesion of soot, and a honeycomb filter
reducing the pressure loss after ash deposition; and a method for
producing a honeycomb filter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view showing a honeycomb filter to which an
embodiment of the present invention is applied and plan view of the
filter.
FIG. 2 is a schematic view showing the honeycomb filter of FIG. 1
and perspective view of the honeycomb filter.
FIG. 3 is a cross-sectional view of the honeycomb filter of FIG. 1
and view shown schematically.
FIG. 4A is a partial cross-sectional view schematically showing a
part of a partition wall of the honeycomb filter in the present
embodiment.
FIG. 4B is a partial cross-sectional view schematically showing a
part of a partition wall of the honeycomb filter in the present
embodiment.
FIG. 5A is a partial cross-sectional view schematically showing a
part of a partition wall of a conventional honeycomb filter.
FIG. 5B is a partial cross-sectional view schematically showing a
part of a partition wall of a conventional honeycomb filter.
FIG. 5C is a partial cross-sectional view schematically showing a
part of a partition wall of a conventional honeycomb filter.
FIG. 5D is a graph showing the relation between the soot deposition
amount and the pressure loss of the partition wall.
FIG. 5E is a partial cross-sectional view schematically showing a
part of a partition wall of a conventional honeycomb filter.
FIG. 6 is a graph showing the relation between the ash deposition
amount and the pressure loss of the partition wall by soot.
FIG. 7 is a graph showing the relation between the soot deposition
amount in each step in engine drive and the pressure loss of the
partition wall by soot.
FIG. 8A is a partial cross-sectional view of a partition wall of a
conventional honeycomb filter and view schematically showing a soot
deposition condition of a partition wall in the initial stage in
engine drive.
FIG. 8B is a partial cross-sectional view of a part of a cell of a
conventional honeycomb filter, schematically showing the soot
deposition condition in FIG. 8A in the cell longitudinal
direction.
FIG. 9A is a partial cross-sectional view of a partition wall of a
conventional honeycomb filter, schematically showing a soot
deposition state of the partition wall in the initial stage in
engine drive.
FIG. 9B is a view schematically showing the soot deposition state
in FIG. 9A in the cell longitudinal direction.
FIG. 10A is a partial cross-sectional view of a partition wall of a
conventional honeycomb filter, schematically showing a soot
deposition state of the partition wall after repeated
regeneration.
FIG. 10B is a view schematically showing the soot deposition state
of FIG. 10A in the cell longitudinal direction.
FIG. 11 is a partial cross-sectional view of a partition wall of
the honeycomb filter of the present embodiment, schematically
showing the outermost contour line.
FIG. 12 is a partial cross-sectional view of a partition wall of
the honeycomb filter of the present embodiment, schematically
showing the outermost contour line.
FIG. 13 is a schematic view showing a honeycomb filter where
another embodiment of the present invention is applied and
perspective view of the honeycomb filter.
DETAILED DESCRIPTION OF THE INVENTION
Hereinbelow, modes for carrying out a honeycomb filter of the
present invention and a method for producing the honeycomb filter
are specifically described. However, the present invention widely
includes honeycomb filters and methods for producing the honeycomb
filters provided with the subject matter of the present invention
and is not limited to the following modes.
[1] Honeycomb Filter of the Present Invention:
As shown in FIGS. 1 to 4A, the honeycomb filter 1 of the present
invention is constituted as a honeycomb filter 1 having a
honeycomb-structured substrate provided with a plurality of cells 3
separated by partition walls 4 of porous ceramic having pores,
wherein plugging portions 13 are formed alternately in one side
open end portions 11a and the other side open end portions 11b of
the plural cells 3, at least in open pores 7 formed by the
particles constituting the partition walls 4 and/or gaps 9 between
the particles, a composite region is formed by depositing particles
5 having an average particle diameter smaller than that of the
particles in a surface layer portion 4a of the partition walls on
the exhaust gas inflow side, the partition walls have an average
pore diameter of 5 to 40 .mu.m and a porosity of 35 to 75%, the
particles deposited have an average particle diameter of 1 to 15
.mu.m, and the composite region has a height of 80 .mu.m or less
with respect to the partition wall surface direction from the
outermost contour line of the partition walls.
[1-1] Composite Region:
The composite region in the present embodiment is formed by
depositing particles having an average particle diameter smaller
than that of the aforementioned particles at least in open pores
formed by the particles constituting the partition wall and/or gaps
between the particles. That is, the composite region is constituted
as a composite layer composed of the particles constituting the
partition wall and the particles deposited on the partition wall by
depositing particles having an average particle diameter smaller
than that of the particles constituting the partition walls at
least in open pores formed by the particles constituting the
partition wall and/or gaps between the particles. The reason why
the composite region is formed in the surface layer portion of the
partition walls on the exhaust gas inflow side is because the
pressure loss incidence rate is reduced to improve the PM trapping
efficiency even without imparting properties of pores having small
average pore diameter to the partition walls. In other words, even
without forming a layer having small average pore diameter to the
partition walls, by forming the composite region of the present
embodiment, the pressure loss incidence rate of partition walls
caused when the exhaust gas passes through the partition walls at
high flow rates can be reduced with obtaining the same effect as in
the formation of a layer having properties of pores having a small
average pore diameter on the partition walls.
That is, by forming the composite region by depositing particles
having an average particle diameter smaller than that of the
particles constituting the partition walls in open pores and/or
gaps between the particles, the particles as so-called "simulated
ash" are deposited in the open pores and/or gaps between the
particles. The particles (particles having an average particle
diameter smaller than that of the particles constituting the
partition walls) as the "simulated ash" inhibit soot and ash from
entering the open pores and/or gaps between the particles.
Therefore, the deposition of soot and ash can be controlled, and
reduction of the pressure loss incidence rate in the partition
walls can be realized.
Further, in the composite region, the particles having an average
particle diameter smaller than that of the particles constituting
the partition walls may be connected to one another in the open
pores formed by the particles constituting the partition walls
and/or gaps between the particles in the surface layer portion of
the partition walls on the exhaust gas inflow side. The thus
connected particles deposit in, for example, pores of the partition
walls on the downstream side with respect to the surface layer of
the particles constituting the partition walls and/or the region on
the upstream side with respect to the surface layer of the
particles constituting the partition walls. The particles connected
to one another form an open pores of the partition walls and/or a
space between the particles smaller than the size (pore size) of
the space of the pores. Further, the particles connected to one
another are present so as to cover a part of or the entire range of
the particles constituting the partition walls and the gaps between
the particles. The particles connected to one another also form the
particle assemblage or particle layer described later.
For example, as shown in FIG. 5A, there is a conventional honeycomb
filter (hereinbelow appropriately referred to as a "conventional
honeycomb filter") composed of a two-layer structure having a layer
having an average pore diameter smaller than that of the partition
wall and formed on the partition walls as an inlet layer 115 and
the partition wall. In comparison with the conventional honeycomb
filter, the difference of the present embodiment is clear.
In the partition walls with which the conventional honeycomb filter
is provided, specifically, there were a case (1) of generating
pressure loss in the partition walls due to deposition of soot in
the partition walls and a case (2) of generating pressure loss in
the partition walls due to deposition of ash in the partition
walls. Further, there was a case (3) of generating pressure loss by
having both (1) and (2) together.
An example of the case (1) of generating pressure loss in the
partition wall due to deposition of soot in the partition walls is
as follows. In the first place, soot enters in the pores which are
partition walls on the exhaust gas inlet side and formed in the
surface layer portion of the partition walls. The soot having
entered in the pores deposits in the pores to have a saturated
state in the pores. Further, after the saturation in the pores,
soot deposits on the partition walls to form a so-called cake
layer. Thus, the pressure loss of the partition walls of (1) could
be caused in the deposition mode where soot deposits.
Description will be given specifically with referring to drawings.
As shown in FIG. 5B, in the initial stage where the engine is
continuously driven a shot time, since the soot 117 does not
sufficiently deposit on or in the partition walls, the soot enters
the pores of the inlet layer 115. That is, as shown in FIG. 5B, the
pressure loss of the partition walls attributed to the soot is
caused by the stress applied to the partition walls when the soot
117 enters the pores to do damage to the partition walls. In other
words, as shown in FIG. 5C, in the case that the soot 117 deposits
sufficiently in the pores to have a saturated state or that the
soot deposits sufficiently on the partition walls to form a cake
layer, soot hardly enters or cannot enter. Therefore, pressure loss
of the partition walls by the soot is hardly caused. This is clear
also from FIGS. 5D and 5E showing the relation between the soot
deposition amount and the pressure loss. In the initial stage of
engine drive, as shown in FIG. 5D, the amount of soot entering the
pores is high, and soot enters in the region of I shown in FIG. 5E
to raise the possibility of causing pressure loss in the partition
walls. However, when the pores have a saturated state after the
soot enters in the pores, or when a cake layer is formed after the
soot deposits on the partition walls, as shown in FIG. 5E, the
state where the soot deposits in the region of II is shown.
Therefore, as shown in FIG. 5D, the amount of soot entering the
pores is reduced, thereby reducing the pressure loss incidence rate
of the partition walls due to entry of the soot. Thus, there is a
high possibility of causing the pressure loss of the partition
walls by the soot in the initial stage where the engine is not
continuously driven. On the other hand, in the stage where the
engine is continuously driven, which is the stage next to the
initial stage, there is a low possibility of causing the pressure
loss of the partition walls. Therefore, the problem was how to
eliminate the possibility of pressure loss of the partition walls
repeatedly caused upon soot combustion in the regeneration control
with trying to reduce pressure loss of the partition walls in the
initial stage.
In addition, as an example of the case (2) of generating pressure
loss in the partition wall due to deposition of ash in the
partition walls, it could happen when ash enters in the pores which
are partition walls on the exhaust gas inlet side and formed in the
surface layer portion of the partition walls, or ash damages the
surfaces of the partition walls in the state that the soot
deposition on the partition walls is insufficient. Specifically, as
shown in FIG. 5A, in the initial stage where the engine is not
driven continuously, soot is not deposited on the partition walls
or in the partition walls. That is, there is no so-called shielding
layer which inhibits ash from entering the pores. Therefore, ash
has various shapes and sizes and easily enters the pores in the
state that no soot is deposited.
Further, ash is discharged from the engine with being mixed in the
soot and flows into the passages (cells) of the honeycomb filter.
Therefore, the deposition modes of soot and ash are simultaneously
performed (3). The deposition modes of soot and ash have two
prominent stages (Phase A and Phase B), and the pressure loss of
the partition walls is caused from the composite factor.
In the first stage (Phase A, hereinbelow appropriately referred to
as the "first state" or "phase A"), there is shown a general
behavior showing that the pressure loss of the partition walls is
caused by the deposition of ash. In this ash deposition pressure
loss behavior is clear from the relation between the pressure loss
of the partition walls attribute to the soot and the amount of ash
shown in FIG. 6. That is, in the engine drive initial stage, since
no soot is deposited in the surface layer portion of the partition
walls on the exhaust gas inflow side, there is a high possibility
of generating pressure loss of the partition walls because soot and
ash are mixed and enter the pores to be deposited (see point a of
FIG. 6).
Next, in the termination of the first stage (Phase A), soot is
combusted by repeatedly regenerating a honeycomb filter. However,
since ash is not combusted, ash gradually deposits in the pores.
Thus, in the termination of the first stage (Phase A), ash
deposited in the pores by the repeated regeneration of the
honeycomb filter inhibits soot from entering the pores. As a
result, the pressure loss of the partition walls is reduced (see
point b of FIG. 6).
Further, when the regeneration of the honeycomb filter is repeated,
ash contained in the soot is sent toward the downstream side of the
cells (inlet cells) open at the inlet of the exhaust gas upon
regeneration. Then, ash deposits on the plugging portions on the
exhaust gas outlet side. Therefore, the effective volume of the
inlet cells is gradually reduced. As a result, the thickness of the
soot layer when a certain amount of soot deposits becomes large,
and the partition wall permeation flow rate (flow rate when exhaust
gas permeates the partition walls) becomes high, thereby raising
the pressure loss of the honeycomb filter (DPF). This corresponds
to the second stage (Phase B, hereinbelow appropriately referred to
as the "second stage" or "phase B") (see Phase B of FIG. 6).
Incidentally, "cell effective volume" means the capacity of the
space where exhaust gas can pass and/or the space in the inlet
cells where the soot can deposit. The smaller cell effective volume
has a higher tendency of rise in exhaust gas permeation flow rate
and a higher tendency of increase in thickness of the soot layer
formed on the partition walls upon soot deposition. Therefore, the
pressure loss incidence rate of the partition walls in the
honeycomb filter (DPF) rises. Here, the exhaust gas permeation flow
rate means the speed when exhaust gas permeates the partition
walls, that is, the speed when the exhaust gas passes through the
pores of the partition walls.
In such two stages (Phase A and Phase B), the pressure loss
incidence rate of the partition walls is hardly reduced, or the
regeneration efficiency is hardly improved. For example, as shown
in FIG. 7 showing the relation between the soot deposition amount
and the pressure loss of the partition walls by soot deposition, in
the initial stage where no ash is deposited of the graph a, as
shown in FIGS. 8A and 8B, since no ash deposits in the pores of the
partition walls, the cell effective volume is sufficient. However,
the pressure loss incidence rate of the partition walls by soot
cannot be reduced sufficiently, which is not preferable. On the
other hand, as shown in the graph c of FIG. 7, in a state where
sufficient ash is deposited (state where the regeneration treatment
is performed repeatedly), the pressure loss incidence rate of the
partition walls by soot can be reduced. However, the cell effective
volume is not sufficient, and soot is sent toward the downstream
side as shown in FIGS. 10A and 10B, which is not preferable.
Therefore, the present embodiment employs not only the two-layer
structure where a layer of particles having an average particle
diameter smaller than that of the particles constituting the
partition walls is formed on the partition walls, but also the
aforementioned structure. For example, the present embodiment
employs a structure where the state of sufficient ash deposition of
the graph b of FIG. 7 is added in advance. By such constitution,
the effect of improvement in the soot combustion and regeneration
efficiency is realized by securing the cell effective volume with
reducing the pressure loss incidence rate of the partition walls as
shown in FIGS. 9A and 9B. Above all, the regeneration efficiency is
improved with reducing the pressure loss incidence rate of the
partition walls regardless of the period of use of the engine.
In other words, in the present embodiment, as shown in FIG. 4A, by
forming the composite region 4a by depositing the particles 5
having an average particle diameter smaller than that of the
particles 4b constituting the partition walls 4 at least in the
open pores 7 formed by the particles constituting the partition
walls 4 and/or gaps 9 between the particles in a surface layer
portion 4a of the partition walls on the exhaust gas inflow side,
soot and ash are inhibited from entering the open pores and/or gaps
between the particles as shown in FIG. 4B.
Here, the aforementioned "partition walls on the exhaust gas inflow
side" means the partition walls formed on the exhaust gas inflow
side in the honeycomb-structured substrate. Specifically, as shown
in FIGS. 3 to 5, the partition walls on the exhaust gas inflow side
correspond with the inlet ports of the exhaust gas inflow passages
in the partition walls 4 which the cells 3 have and the region in
the vicinity of the inlet ports.
In addition, the "surface layer portion" of the partition walls on
the exhaust gas inflow side means the region on the exhaust gas
inflow side in the region in the partition wall thickness direction
and the region in the vicinity of the region. Specifically, as the
region 4a shown in FIG. 4A, the region is the region on the exhaust
gas inflow side in the region in the partition wall thickness
direction on the exhaust gas inflow side and the region in the
vicinity of the region.
In addition, the "particles constituting the partition walls"
means, for example, ceramic particles.
In addition, the "open pores" formed by particles constituting the
partition walls means the pores which the exhaust gas can enter
without being closed among the pores formed by the particles such
as the aforementioned ceramic particles. In other words, the
"closed pores" which the exhaust gas cannot enter with being closed
are excluded even if the pores are formed by the aforementioned
particles. An example is an open pore which exhaust gas can flow in
and flow out without being closed if particles do not deposit as
the pore shown by the reference numeral 7 in FIG. 4A.
In addition, the "gap between particles" formed by the particles
constituting the partition walls means the gaps formed between the
particles formed by the particles such as the aforementioned
ceramic particles and gaps exhaust gas can enter without being
closed and formed between the particles. In other words, the gap
which exhaust gas cannot enter with being closed are excluded even
if the gap is formed between the aforementioned particles. An
example is a gap formed between the particles (R1, R2) if particles
are not deposited as the region shown by the reference numeral 9 of
FIG. 4A.
Incidentally, the reason of specifying the matter to the open pores
"and/or" gaps between the particles is because the pressure loss of
the partition walls can be reduced even by depositing the particles
in either the open pores or the gaps between the particles as the
composite region though it is desirable that the composite region
is formed in both the open pores and the gaps between the
particles. However, it is more preferable that particles are
deposited in both the open pores and the gaps between the particles
as the composite region.
In addition, the reason why the particles having an average
particle diameter smaller than that of the particles constituting
the partition walls are deposited at least in the open pores formed
by the particles constituting the partition walls and/or the gaps
in the surface layer portion of the partition walls on the exhaust
gas inflow side is because, even if deposition of the particles
having an average particle diameter larger than that of the
particles (e.g., ceramic particles) constituting the partition
walls is tried, the particles hardly deposit in the open pores
and/or gaps between the particles and hardly stay in the gaps.
Further, the open pores and the gaps between the ceramic particles
cannot be clogged sufficiently. As a result, it becomes hard to
sufficiently trap soot in the composite region. In addition, soot
passes through the composite region to easily deposit in the pores
of the partition walls formed on the downstream side of the
composite region. Therefore, soot deposition similar to the case of
the conventional partition wall having two-layered structure is
caused, and there is a high possibility of causing pressure loss in
the partition walls. Thus, the particles to be deposited hardly
play a role as the aforementioned "simulated ash".
On the other hand, when the average particle diameter of the
particles to be deposited is smaller than the average particle
diameter of the particles constituting the partition walls,
adhesion to the aforementioned open pores and/or gaps between the
particles becomes easy. However, when the average particle diameter
of the particles to be deposited is too small, the particles having
the small average particle diameter pass through the open pores
and/or gaps between the particles in the surface layer portion of
the partition walls on the exhaust gas inflow side. In addition,
the particles may deposit inside the partition walls other than the
aforementioned open pores and/or gaps between the particles.
Therefore, in the inside of the partition walls, the connection
portion of the pores of the partition walls is locally clogged, and
the gas permeability at the time when exhaust gas permeates the
partition walls is prone to be deteriorated. By the low gas
permeability, the pressure loss incidence rate in the partition
walls is raised to a great extent, which is not preferable.
Therefore, it is desirable to form the composite region by
adjusting the particles to be deposited to have an appropriate size
(average particle diameter).
Here, "connection portion" of the pores of the partition walls
means a portion where the distance between the particles is the
smallest and where the inner diameter of the pore is the smallest
in the case of forming gaps (spaces), i.e., pores between the
particles by connecting the particles as SiC. In other words, it
means a portion where the diameter of the exhaust gas passage is
the smallest.
Incidentally, since the size of soot is generally about 100 nm on
an average, and the size of ash is about 1 .mu.m on an average, it
is preferable that the particles to be deposited have appropriate
sizes which soot these sizes.
In addition, the "particles having an average particle diameter
smaller than the average particle diameter of the particles" means
the particles to be deposited in the open pores and/or gaps between
the particles has an average particle diameter smaller than the
average particle diameters of the particles constituting the
partition walls. Each of the diameters of the particles
constituting the partition walls and the diameters of the particles
constituting the composite region can be calculated by the image
analysis from the photograph of a polished face or a fracture face
of a SEM. Incidentally, the contribution to the reduction of
pressure loss with soot (partition wall pressure loss caused by the
deposition of soot in pores) basically depends on the absolute
value of the particle diameter of particles forming the composite
region and the deposition state and deposition distribution in the
composite region of particles having an average particle diameter
smaller than that of particles. Therefore, it is not determined
only by the ratio of the average particle diameter of the particles
having an average particle diameter smaller than that of the
particles constituting the composite region to the average particle
diameter constituting the partition walls. That is, even if
particles constituting the same composite region are used, in the
case that the average pore diameter of the partition walls is very
large, or in the case that the porosity of the partition walls is
very high, the particles (deposited particles) having an average
particle diameter smaller than the average particle diameter of the
particles constituting the partition walls do not stay in the
composite region, and many particles enter the pores of the
partition walls other than the composite region to easily clog
pores. Therefore, there may be caused a defect such as remarkable
rise of the pressure loss incidence rate of the partition walls.
Accordingly, it is preferable to deposit desired "particles having
an average particle diameter smaller than that of the particles"
according to the absolute value of the diameter of the particles
forming the composite region, the deposition condition, and the
deposition distribution.
Further, it is preferable to form the aforementioned composite
region by depositing the particles having an average pore diameter
smaller than the average size of the open pores formed by particles
constituting the partition walls and/or the gaps between the
particles. By depositing the particles having an average pore
diameter smaller than the average size of the open pores formed by
particles constituting the partition walls and/or the "gaps"
between the particles, the composite region can be densified in
comparison with the partition walls, which is preferable. Further,
necessary and sufficient particles can be filled more efficiently
in the open pores and/or gaps between the particles, soot can
efficiently be inhibited from entering the pores of the partition
walls.
[1-1-1] Particles to be Deposited (Simulated Ash):
The composite region of the present embodiment is formed by
depositing particles having an average particle diameter smaller
than that of the particles at least in the open pores formed by the
particles constituting the partition walls and/or gaps between the
particles. That is, "particles to be deposited" constitute a part
of the composite region and are deposited on the partition walls as
"simulated ash" as described above (hereinbelow, the "particles to
be deposited" are appropriately referred to as "simulated ash"). By
depositing particles as simulated ash, soot and ash can be
inhibited from entering the open pores and/or the gaps between the
particles in the composite region even in the engine initial
rotational state where the soot and ash do not deposit on the
partition walls or in the pores of the partition walls. Therefore,
pressure loss of the partition walls can be inhibited from being
caused.
In addition, the soot inhibited from entering the open pores and/or
the gaps between the particles by the particles as the simulated
ash is combusted upon regeneration. Therefore, since soot does not
deposit even by the repeated regeneration, the effective area of
the honeycomb filter is not reduced. Further, no influence is
received from the engine drive time or the deposition mode of soot
and ash. In other words, regardless of the engine start-up time or
the continuous drive time, the pressure loss incidence rate of the
partition wall can be reduced. In addition, since soot can be
inhibited from entering the pores of the partition walls, ash
contained in the soot, particularly, sulfur component contained in
the ash can be inhibited from contacting the catalyst even in the
case that a catalyst is loaded in the pores of the partition walls.
Therefore, the catalyst can be inhibited from deteriorating.
In addition, the average pore diameter of the particles deposited
in the open pores and/or the gaps between the particles is 1 to 15
.mu.m. The average pore diameter of the particles deposited is
preferably 1 to 5 .mu.m. When it is smaller than 1 .mu.m, since the
packing density in the pores of the partition walls becomes high to
fill the pores, the pressure loss incidence rate of the partition
walls is raised. When it is larger than 15 .mu.m, since the space
region between the particles forming the pores cannot be clogged
efficiently, PM easily passes through the space region between the
particles forming the partition walls and the composite
region-forming particles. Therefore, sufficient trapping efficiency
cannot be obtained. Incidentally, the average diameter of such
particles can be measured by an image analysis with observing the
resin-embedded polished surface or a fracture face by a SEM.
The height of the composite region is 80 .mu.m or less with respect
to the partition wall surface direction from the outermost contour
line of the partition walls. This enables the particles to easily
stay in the open pores and/or the gaps between the particles. In
other words, the deposited particle hardly flows toward the
adjacent cell side (so to speak, exhaust gas outlet side) on the
downstream side of the composite region from the open pores and/or
the gaps between the particles when the exhaust gas flows into the
partition walls and flows out from the partition walls. Further,
the hydraulic diameter of the cell inlet (unplugged cell serving as
an inlet for exhaust gas) can be secured sufficiently. Above all,
pressure loss of the partition walls in the region (high flow rate
region) where exhaust gas passes at high flow rates can be
inhibited. On the other hand, when it is larger than 80 .mu.m, the
hydraulic diameter of the cell inlet becomes small to raise the
pressure loss incidence rate of the partition walls particularly in
the high flow rate region, which is not preferable. It is more
preferably 30 .mu.m or less.
Incidentally, the aforementioned composite region may be
constituted of a particle assemblage where the particles to be
deposited form an assemblage, or, a particle layer where particle
assemblages are connected to one another to form a layer. In the
particle assemblages, for example, an assemblage of particles where
the particles to be deposited are formed of plural particles or an
assemblage where particles are connected to one another is
included. On the other hand, by a thermal treatment, that is,
addition of pore former and the like upon subjecting the material
to reaction sintering, the pore structure formed is eliminated. In
other words, it means the state where the pore structure formed by
connecting the spaces (pores) formed by the pore former is
eliminated to allow the assemblages of particles to be dispersed
(sprinkled) as an assemblage in the open pores and/or the gaps
between the particles. Examples of the formation of the particle
assemblages are the formation by mixing silica or the like in
ceramic particles or the like and the formation by depositing only
simple ceramic particles on the partition walls. However, the
formation is not limited to these.
In addition, the "outermost contour line of the partition wall"
means a supposition line (virtual line) for separating a partition
wall and a cell and contour line located on the outermost side
among the lines forming the contour line of the partition wall.
That is, the "outermost contour line of the partition wall" means
the outermost contour line of the partition wall and supposition
outermost contour line formed upon connecting the points where a
particle forming the outer contour line is separated from the
projection line. Further, when the pores are formed with particles
separating from one another, the virtual line obtained by drawing a
line parallel to the surface layer reference line described later
from a point separated from the projection line on the surface of
each particle corresponds to the "outermost contour line".
Specifically, each of the particles forming the outermost contour
line of the partition walls is present in the partition wall which
is the nearest to the boundary separating the passage (cell) where
a fluid flows from the partition wall, and the suppositional
contour line obtained by connecting the particles serves as the
"outermost contour line". In the case that the particles each
forming the outermost contour line of the partition are not
adjacent to each other to form a pore, the supposition line formed
by drawing a line parallel to the surface layer reference line to
connect the points where each of the partition walls separated from
each other separates from the projection line serves as the
"outermost contour line". Further, though the partition wall
appears to be formed into an almost flat and smooth plate shape by
eye observation, it can be confirmed that numerous irregularities
are formed on the contour of the partition walls. It is preferable
to deposit the particles, particle assemblages, and particle layer
in the region from the supposition line obtained by connecting,
parallel to the surface layer reference line, the points where the
aforementioned particles in the region along the concave or convex
contour of the partition walls having numerous irregularities
separate from the projection line in the pores to at least the
surface of the partition wall.
In addition, the "surface layer reference line" shows the average
height of the irregularities of the surface layer in one visual
field.
Therefore, "the composite region has a height of 80 .mu.m or less
with respect to the partition wall surface direction from the
outermost contour line of the partition walls" means that, in the
case that the particles to be deposited in the open pores and/or
the gaps between the particles form the aforementioned composite
region, the particles are present in the region (open pores and/or
the gap between the particles) within 80 .mu.m in the partition
wall thickness direction (direction perpendicular to the partition
wall) from the outermost contour line of the partition wall toward
the partition wall surface. Incidentally, in the case that the
particles to be deposited in the open pores and/or the gaps between
the particles form the aforementioned composite region as particle
assemblages of assemblages, it means that the particle assemblages
are present in the region within 80 .mu.m in the partition wall
thickness direction (direction perpendicular to the partition wall)
from the outermost contour line of the partition wall toward the
partition wall surface. In addition, the same can be applied to the
particle layer. In addition, the same can be applied to the case
where the particles, particle assemblages, and particle layers are
present together to form the composite region. Further, the "height
of the composite region" means the distance from the point where
the particle forming the composite region is farthest in the
partition wall thickness direction (direction perpendicular to the
partition wall) (point where the particle forming the outermost
contour line is farthest from the projection line) with the
outermost contour line of the partition wall as the base to the
outermost contour line.
As a specific measurement method of the "height of the composite
region", a resin-embedded polished cross section or a fracture
surface is observed by a SEM, and an image analysis is performed
for the measurement. In the image analysis, the outermost contour
line of the partition wall is drawn, and then a line parallel to
the outermost contour line in the partition wall thickness
direction (direction perpendicular to the partition wall) is drawn.
Then, the line parallel to the outermost contour line is gradually
raised toward the upstream side (partition wall perpendicular
direction side) for observation. In the observation visual field,
the point where the particle assemblage separates from the line
parallel to the outermost contour line is obtained for the
measurement with the distance from the outermost contour line of
the partition wall as the composite region height.
Specifically, the outermost contour line 17 having irregularity can
be shown in FIG. 11. At least particles are deposited in the region
of 80 .mu.m or less from the outermost contour line in the
partition wall surface direction. More specifically, as shown in
FIG. 12, the outermost contour means the contour obtained when the
particles 99a forming the outermost contour of the partition wall
is connected to the point P where the projection line is separated.
Further, in the case that particles are separated from each other
to form a pore, the supposition line obtained by drawing the
parallel line I parallel to the surface layer reference line H from
the point P where the particle surface separates from the
projection line and further drawing a perpendicular line from the
point P to connect with the aforementioned parallel line I is
referred to as the outermost contour line. Incidentally, the
reference symbol J shown in the figure shows a projection line to
the surface layer reference line.
Incidentally, though the outermost contour line shown in FIG. 11 is
drawn as a supposition line like a belt, it is for the convenience
of description, and, needless to say, such a supposition line is
not shown in the honeycomb filter of the present embodiment.
In the case, regarding the surface layer reference line, the
"composite region depth" and "composite region depth rate" in the
present specification mean the following content, respectively.
The "composite region depth" means the depth of entry of the
particles to be deposited from the aforementioned surface layer
reference line toward the down stream side in the partition wall
thickness direction in the partition wall surface layer having
irregularity. The "composite region depth" can be measured by the
following technique. In the first place, a sample obtained by
subjecting the partition wall base material to resin-embedded
polishing is prepared in advance, and the surface layer reference
line is obtained by an image analysis or the like in a SEM
observation. Next, from the surface layer reference line, the depth
of the entry of the particles deposited on the downstream side of
the partition wall is measured. Thus, the maximum entry depth in
one visual field of the SEM is determined as the composite region
depth in the measurement.
The "composite region depth rate" means the proportion of the
aforementioned composite region depth with respect to the partition
wall depth. Here, the "partition wall thickness" means the distance
between the partition wall surface on the upstream side and the
partition wall surface on the downstream side. More strictly
speaking, it is shown by the distance between the surface layer
reference lines on the upstream side and on the downstream side.
For the measurement of the partition wall thickness, a sample
obtained by subjecting the partition wall base material to
resin-embedded polishing is prepared in advance in the same manner
as in the measurement of the composite region depth. Further, by
obtaining the surface layer reference lines on the upstream side
and the downstream side in the SEM observation of the polished face
of the sample, the "composite region depth rate" can be
measured.
Incidentally, each of the measurements of the "composite region
depth" and the "composite region depth rate" is performed as
follows. As shown in FIG. 3, measurement is performed at three to
five points in total in the central portion and outer peripheral
portion in a cross section perpendicular to the axial direction
with respect to the radial direction in the central portions of the
upstream portion (exhaust gas inflow side Z1), mid-stream portion
(mid-stream portion Z2 (mid-stream region Z2), and the down stream
portion (exhaust gas outflow side Z3) with respect to the axial
direction of the honeycomb filter. The average value of the
measurement data at 9 to 15 points in total is determined as the
measurement value of the honeycomb filter to be measured. The
upstream potion, the mid-stream portion, and the downstream portion
are trisected, and the measurement is performed in the central
portion of each section. Regarding the radial direction, the region
on the central side with respect to the center of the radius is
determined as a central portion, and the region on the outside with
respect to the center of the radius is determined as the outer
peripheral portion in the radius of a cross section, and the
measurement is performed at three to five points of each of the
regions. Here, the aforementioned "radial direction" means the
outside direction in a cross section perpendicular to the axial
direction of the honeycomb filter and is not limited to the meaning
of the words. This is because not only the case that the cross
section perpendicular to the axial direction of the honeycomb
filter is circular, but also the case that the cross section is
oval and the case that the cross section is irregular are
included.
In addition, it is preferable that the composite region is formed
in the open pores and/or the gaps between the particles in the
range from the surface layer reference line of a partition wall on
the exhaust gas inflow side to 30% of the partition wall thickness.
This is because, when the particles deposited is above 30% in the
partition wall thickness direction, the deposited particles begin
to clog the neck portions of the partition wall pores, and the
possibility of causing pressure loss of the partition wall rises.
That is, when the "neck portion" of a partition wall pore is
clogged, exhaust gas cannot permeate the partition wall to make the
flow of the exhaust gas into the adjacent cell though the partition
wall difficult. This state raises the (inflow and outflow) pressure
when exhaust gas passes through the partition wall (make the gas
permeability low) and the stress applied to the partition wall
increases. Therefore, the pressure loss of the partition wall is
easily caused.
Here, the "[neck portion] of partition wall pore" means the region
where the size of the pore is small in the distribution of pores in
the partition wall and region where the inner diameter of the duct
line is small. For example, the region is shown by the symbol N in
FIG. 4A. In addition, "the deposited particles begin to clog the
neck portions of the partition wall pores" means that the clogging
of the neck portions is increased by the formation of the composite
region to narrow the exhaust gas passage by the clogging. Thus,
when "the deposited particles begin to clog the neck portions", the
gas permeability falls to increase pressure loss.
Further, it is preferable that the composite region is formed in
the open pores and/or the gaps between the particles from the
surface layer reference line of the partition wall on the exhaust
gas inflow side to the depth up to 4 times the average pore
diameter of the partition wall. When it is larger than 4 times, the
particles forming the composite region begin to clog a neck portion
in the open pores and/or the gap between particles, and pressure
loss rises. When the clogging in neck portions of partition wall
pores increases, the pressure loss rises, which is not
preferable.
Here, the "open pores and/or the gaps between the particles to the
depth up to 4 times the average pore diameter of the partition
wall" means the open pores and/or the gaps between particles formed
in the region to the depth (partition wall thickness) of 4 times
the average pore diameter of the partition wall or less in the
partition wall thickness direction. For example, when the average
pore diameter of the partition wall is 15 .mu.m, they mean the open
pores and/or the gaps between particles formed up to about 60 .mu.m
in the partition wall thickness direction.
In addition, it is preferable that the particles to be deposited in
the open pores and/or the gaps between the particles are of the
same material as that for the particles constituting the partition
walls. In the case that the particles to be deposited in the open
pores and/or the gaps between the particles are formed of the same
material as that for the particles constituting the partition
walls, not only the adjustment of durability and stress is easy,
but also the formation is simple, which is preferable. Further, a
unit price of the product can be reduced, which is preferable.
Here, "formed of the same material as that for the particles
constituting the partition walls" means that, for example, in the
case that the partition walls are formed of silicon carbide or a
composite material of silicon carbide and silicon, the particles
formed of silicon carbide serving as the framework of the partition
walls are deposited.
In addition, it is preferable that the particles constituting the
partition walls are of silicon carbide or a composite material of
silicon carbide and silicon. By the connection of particles
constituting a partition wall, a pore of the partition wall is
formed. Therefore, pores of the partition walls are formed by the
connection of the particles constituting the partition walls.
Therefore, no closed pore is substantially present in the partition
walls, and most pores of the partition walls are communicated
pores. Therefore, upon depositing the particles having an average
particle diameter smaller than the average particle diameter of the
particles constituted of the partition walls, the particles are
easily deposited in the open pores of the particles and/or the gaps
between the particles.
One of the preferable embodiments is that the particles deposited
in the open pores and/or the gaps between the particles are
connected with one another by a connection phase different from the
framework particles constituting the partition walls. The
embodiment is preferable because, in the case of the same
connection material, there may infrequently be caused a negative
effect of remarkable clogging of the pores by the connection of the
connection phases upon being exposed at high temperature for a long
period of time. Therefore, such a defect in the production process
can be inhibited before it happens.
Further, it is preferable that particles deposited in the open
pores and/or the gaps between particles are connected by a silica
phase. In the composite region, since the contact of the particles
deposited in the pores and/or the gaps of the partition walls with
the soot entering therein increases, the temperature rise by the
extraordinary local combustion of the soot upon regeneration tends
to increase. However, by connecting the particles by the silica
phase, the thermal resistance of the composite region is increased,
and the reactivity resistance against ash or sulfur component can
be improved. Therefore, the durability of the composite region
becomes high, which is preferable. Specifically, in the case that
the partition wall base material is of silicon carbide or a
composite material of silicon carbide and silicon, by the thermal
treatment in the ambient atmosphere or the like, the silica phase
is formed on the surface of the particles of the particle
assemblage constituted of the silicon carbide. Therefore, it is
possible to connect the silicon carbide particles together, or the
silicon carbide particles to the base material constituted of a
silicon carbide or a composite material of silicon carbide and
silicon. Thus, there can be formed the composite region adhering to
the partition wall base material or particle assemblages depositing
on and adhering to the partition walls described later are
formed.
Incidentally, in the case of forming a silica phase, the ratio of
the amount of silica to be used is preferably 0.5 to 5.0 mass % of
the total amount of the partition walls and the particle
assemblages deposited on the partition walls. Preferable strength
or thermal conductivity of the partition walls can be obtained, and
preferable adhesion strength of the particle assemblage to be
deposited can be obtained. The thickness of the silica on the
surfaces of the particles constituting the particle assemblage is
preferably 0.1 to 5 .mu.m. When it is smaller than 0.1 .mu.m, since
the bonding force between the particles is not sufficient, peeling
of the particle assemblage may be caused. When it is larger than
0.5 .mu.m, a crack may be caused between the particles by the
thermal expansion at high temperature to cause peeling of the
particle assemblage. Incidentally, "peeling of the particle
assemblage" includes both the case that one particle and/or small
particle assemblage is peeled by the peeling of a part of the
bonding of the particles in the particle assemblage and the case
that the peeling is caused at the interface between the particle
assemblage and the partition wall by the peeling at the bonding
point between the particle and the particle constituting the
partition wall. In addition, the aforementioned "silica thickness"
is measured by a SEM image after the confirmation of silica phase
by the EDX analysis in the first place by the SEM observation of
the resin-embedded polished surface. Incidentally, EDX stands for
Energy Dispersive X-ray Spectroscopy.
[1-2] Honeycomb-Structured Body:
The honeycomb-structured substrate in the present embodiment is a
honeycomb-structured base material provided with a plurality of
cells separated by partition walls 4 of porous ceramic having
numeral pores and functioning as exhaust gas passages as shown in
FIGS. 1 to 3. The honeycomb-structured substrate is constituted as
a honeycomb filter where the partition walls 4 of the cells 3 each
have the upstream layer 13 on the exhaust gas upstream side and the
downstream layer 15 on the downstream side. Incidentally, a
catalyst may be loaded on the honeycomb filter as necessary to
obtain a catalyst-loaded filter.
In addition, plugging portions may be formed to alternately plug
the open end portions 11a on one side and the open end portions 11b
on the other side of plural cells.
Incidentally, the entire shape of the honeycomb structure is not
particularly limited and may be a quadrangular columnar shape, a
triangular columnar shape, or the like as well as a circular
cylindrical shape as shown in FIGS. 1 and 2.
In addition, examples of the shape of the cells (cell shape in a
cross-section perpendicular to the cell formation direction) the
honeycomb-structured substrate includes a square shown in FIG. 1, a
hexagon, and a triangle. However, the shape is not limited to such
a shape, and known cell shapes can widely be included. Amore
preferable cell shape is a circle or a polygon having four or more
angles. The reason why a circle or a polygon having four or more
angles is preferable is because the thickness of the catalyst layer
can be made uniform by decreasing the thick catalyst in a corner
portion in the cell cross section. Above all, in consideration of
cell density, open ratio and the like, a hexagonal cell is
suitable.
Though there is no particular limitation on the cell density the
honeycomb-structured substrate is provided with, in the case of use
as a catalyst-loaded filter of the present embodiment, it is
preferably 0.9 to 233 cells/cm.sup.2. In addition, the thickness of
partition walls is preferably 20 to 2000 .mu.m.
In addition, the porosity of the partition walls the
honeycomb-structured substrate is provided with is 35 to 75%. When
the porosity of the partition walls is lower than 35%, the gas
permeability of the partition walls remarkably falls. The pressure
loss incidence rate of the partition walls (increase in pressure
loss generation in the partition walls) to the soot deposition
amount (soot deposition increase amount) shows a tendency to
increase in a linear form. However, in a state that soot does not
deposit because of remarkably low gas permeation, the pressure loss
incidence rate of the partition walls shows a tendency of further
rise, which is not preferable. In addition, when the porosity is
higher than 75%, the material strength falls, and a crack may be
caused upon canning, which is not preferable.
In addition, it is preferable that the particles constituting the
base material have an average particle diameter of 5 to 60 .mu.m.
When it is smaller than 5 .mu.m, the number of particles present in
a certain volume increases, and contact points between the
particles increases. Therefore, upon firing the
honeycomb-structured substrate, wettability of the contact points
between the particles becomes strong, and as a result the pore
tends to become remarkably small. Therefore, the pores are hardly
formed, and the pressure loss incidence rate of the partition wall
may rise to a large extent. In addition, when the average particle
diameter of the particles constituting the base material is smaller
than 5 .mu.m in the case that particles are bonded with a bonding
phase having a thermal conductivity lower than that of the
particles, the bonding points between the particles become too many
to deteriorate thermal conductivity, which increases a temperature
distribution at high temperature. As a result, a crack may be
caused. On the other hand, when it is larger than 60 .mu.m, the
bonding force falls because of the small number of the bonding
points between the particles, and the strength of the base material
falls. Therefore, a crack may be caused upon canning the honeycomb
filter or upon regeneration. Incidentally, it is preferable that
the porosity of the composite region is lower than that of the base
material of the partition walls and that the porosity of the layer
of the particle assemblages depositing on the partition walls is
higher than that of the composite region. Such a constitution
enables to rise the PM trapping efficiency of the honeycomb filter
and to suppress the rate of occurrence of the pressure loss of the
partition walls.
More specifically, setting can be performed in such a manner that
the porosity of the partition walls is 35 to 75%, that the porosity
of the composite region formed in the partition walls on the
downstream side with respect to the surface layer reference line is
lower than that of the partition walls by 5 to 30%, that the
porosity of the particle layer of particle assemblages deposited on
the upstream partition wall surface layer side with respect to the
surface layer reference line (upstream partition wall surface side
with respect to the surface layer reference line) is larger than
that of the composite region formed in the partition walls on the
downstream side with respect to the surface layer reference line by
5 to 40%, and that the porosity of the particle layer of particle
assemblages deposited on the partition walls is 50 to 90%. When the
porosity of the composite region formed on the partition walls on
the downstream side with respect to the surface layer reference
line is lower than the porosity of the partition walls by 5 to 30%,
the necessary and sufficient exhaust gas passages can be secured,
and the sufficient soot trapping performance can be secured. By
securing the soot trapping performance, soot can be inhibited from
passing through the composite region. By inhibiting the soot from
passing through the composite region, the pressure loss incidence
rate of the partition walls upon soot deposition due to soot
deposition in the base material pores (pores of the partition
walls) in the region below the composite region.
That is, when the fall of the porosity of the composite region in
comparison with the partition walls outside the composite region is
smaller than 5%, the composite region is not formed sufficiently.
Therefore, soot passes through the composite region and deposits in
the pores of the partition walls in the region below of the
composite region. When soot deposits in the pores of the partition
walls in this region, the pressure loss incidence rate of the
partition walls rises to a large extent. In addition, when the fall
of the porosity of the composite region in comparison with the
partition walls outside the composite region is larger than 30%,
the composite region is densified. As a result, the gas
permeability falls to raise the pressure loss incidence rate of the
partition walls to a large extent particularly in the high flow
rate region (region where exhaust gas passes at high flow rates).
In addition, when the porosity in the composite region above the
surface layer reference line is higher than 40% with respect to the
porosity in the composite region below the surface layer reference
line, the change in porosity in the vicinity of the surface layer
reference line becomes too large. As a result, since the bonding
points between the particles decrease, peeling of a particle or a
particle assemblage is easily caused in the vicinity of the surface
layer reference line. In addition, when the porosity of the
particle assemblage deposited in the composite region above the
surface layer reference line in the composite region above the
surface layer reference line or the particle layer of the particle
assemblage deposited is smaller than 50%, since the flow rate of
the soot passing through the pores upon the soot deposition in the
gaps (space) between the particles is high, the pressure loss
incidence rate of the partition walls rises to a large extent. In
addition, when the porosity of the particle assemblages deposited
in the composite region above the surface layer reference line or
the particle layer of the particle assemblages is higher than 90%,
the bonding points between the particles decrease extremely in the
same manner as described above. As a result, the bonding strength
of the particle assemblage falls, and peeling may be caused when it
is exposed to high flow rate conditions (in the case that exhaust
gas passes at high flow rates).
Incidentally, the porosity of the composite region is binarized in
the image analysis of the SEM observation photograph of a
resin-embedded polished surface, and the rate of the gaps (spaces)
between the particles is determined as the porosity.
In addition, the "average pore diameter" and "porosity" of the base
material of the partition walls in the present specification mean
the average pore diameter and the porosity measured by mercury
penetration method. The average pore diameter and the porosity of
the particle assemblage deposited in the composite region or on the
partition walls are measured by appropriately adding the
measurement evaluation by subjecting an image taken by a SEM
(scanning electron microscope) the binarization treatment.
Specifically, the "average pore diameter" of the partition wall
base material is determined by measuring the partition wall base
material by mercury penetration method. When the pore distribution
obtained by the measurement has two peaks, the pore diameter having
the largest pore capacity of the distribution having a larger pore
size is determined as the average pore diameter of the partition
wall base material. On the other hand, in the case that the pore
distribution obtained has only one peak and that the pore
distribution of the partition wall base material cannot be
identified, a desired region of a cross section perpendicular to
the axial direction of the partition wall is subjected to
resin-embedded polishing, the SEM (scanning electron microscope)
observation is performed in the visual field of 100 to 1000
magnifications, and the image obtained is binarized to measure the
average pore diameter of the partition wall base material. In the
same manner, the "porosity" of the partition wall base material is
measured in such a manner that a desired region of a cross section
perpendicular to the axial direction of the partition wall is
subjected to resin-embedded polishing, the SEM (scanning electron
microscope) observation is performed in the visual field of 100 to
1000 magnifications, and the image obtained is binarized to obtain
the porosity from the area ratio of the gaps to the particles in
one visual field. In addition, the "particle diameter" of the
partition wall base material is measured by the SEM image analysis
as in the aforementioned measurements of the pore size and the
porosity in the composite region. The maximum inscribed circle
distribution is obtained with respect to the outermost contour of
the particles constituting the base material, and the diameter
distribution of the maximum inscribed circle is obtained. The
maximum inscribed circle having a diameter smaller than 1 .mu.m is
determined that it is not a particle region, and D50 in the maximum
inscribed circle distribution is determined as the average particle
diameter of the base material.
Incidentally, "D50" means the size of the "50th" particle when
particle diameters measured are aligned in order of size to
determine the largest particle as the 100th particle.
Incidentally, it is preferable to have a relation where the average
pore diameter of the composite region is made smaller than the
average pore diameter of the partition walls and where the particle
layer formed of particle assemblages deposited on the partition
walls is made smaller than the average pore diameter of the
composite region. Such constitution enables to raise the PM
trapping efficiency in the honeycomb filter and suppress the
pressure loss incidence rate of the partition walls. For example,
the setting may be performed in such a manner that the average pore
diameter of the partition walls is 10 to 20 .mu.m, that the average
pore diameter of the composite region is 5 to 10 .mu.m, that the
average pore diameter of the particle layer formed of particle
assemblages deposited on the partition walls is 1 to 5 .mu.m, and
that each of the average pore diameter of the partition walls, the
average pore diameter of the composite region, and the average pore
diameter of the particle assemblages deposited on the partition
walls and particle layers has the size relation among the
aforementioned three average pore diameters.
Further, it is preferable that the thickness of the partition walls
which the honeycomb-structured substrate is provided with is 200 to
600 .mu.m. When it is smaller than 200 .mu.m, soot deposited upon
regeneration easily causes extraordinary combustion. Therefore, the
internal temperature of the honeycomb filter or the internal
temperature of the DPF when the honeycomb filter used as DPF rises,
and a crack may be caused. On the other hand, when it is larger
than 600 .mu.m, the hydraulic diameter becomes too small, and the
pressure loss incidence rate of the partition walls may rise.
Further, in a honeycomb filter of the present embodiment, it is
preferable to have a structure where open end portions on one side
and open end portions on the other side of the plural cells of the
honeycomb-structured substrate are alternately plugged. For
example, as shown in FIG. 3, the structure may be formed in such a
manner that a honeycomb-structured body having plural cells 3
separated by partition walls 4 of porous ceramic having numeral
pores and functioning as exhaust gas passages is employed as a base
material and that the one side open end portions 11a and the other
side open end portions 11b of the plural cells 3 are alternately
plugged by plugging portions 8. In such a honeycomb-structured
body, the exhaust gas G.sub.1 is sent from the opening exhaust gas
inflow cells 3 in the exhaust gas inflow side end face 7a,
particulates in the exhaust gas G.sub.1 are trapped by the
partition walls 4 when the exhaust gas G.sub.1 passes though the
partition walls 4. Further, the exhaust gas G.sub.2 from which the
particulates are removed moves toward the exhaust gas outflow side
end face 7b and is discharged outside of the honeycomb filter from
the opening exhaust gas outflow cells 3.
Though there is no particular limitation on the material of the
honeycomb-structured substrate, the ceramic can suitably be used,
and silicon carbide (recrystallized silicon carbide, silicon-bonded
silicon carbide, etc.) is preferable from the viewpoint of
strength, thermal resistance, corrosion resistance, and the
like.
In addition, the honeycomb-structured substrate can be obtained in
such a manner that an organic binder (hydroxypropoxylmethyl
cellulose, methylcellulose, etc.), a pore former (graphite, starch,
synthetic resin, etc.), and a surfactant (ethylene glycol, fatty
acid soap, etc.) are mixed as desired with the ceramic framework
particles and water, and they are kneaded to obtain kneaded clay,
the kneaded clay is formed into a desired shape and dried to obtain
a formed body, and the formed body is fired.
In addition, an oxidation catalyst, other catalysts, and a
purification material (hereinbelow, appropriately referred to as
"catalyst and the like") may be loaded on a part of or the entire
partition walls of the honeycomb-structured substrate and/or a part
of or the entire composite region. That is, the catalyst and the
like may be loaded on a part of or the entire partition walls, and
the catalyst and the like may be loaded on a part of or the entire
composite region. Further, a catalyst may be loaded on a part of or
the entire partition walls and a part of or the entire composite
region. In addition, for example, there may be loaded a NOx
adsorber catalyst having an alkali metal (Li, Na, K, Cs, etc.) or
an alkali earth metal (Ca, Ba, Sr, etc.), a ternary catalyst, an
auxiliary catalyst represented by an oxide of cerium (Ce) and/or
zirconium (Zr), HC (hydrocarbon) adsorber, or the like.
For example, the PM removal catalyst may contain Ce and at least
one rare earth metal, alkali earth metal, or transition metal.
Here, the rare earth metal can be selected from, for example, Sm,
Gd, Nd, Y, Zr, Ca, La, and Pr.
In addition, the alkali earth metal contained in the PM removal
catalyst can be selected from, for example, Mg, Ca, Sr, and Ba.
In addition, the transition metal contained in the PM removal
catalyst can be selected from Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, V,
and Cr.
In addition, there is no particular limitation on the loading
method of the catalyst component such as an oxidation catalyst and
a NOx adsorber catalyst. An example of the method is a method
where, after the partition walls of the honeycomb-structured body
is subjected to wash coating with a catalyst solution containing a
catalyst, it is subjected to a thermal treatment at high
temperature for baking. Incidentally, the average pore diameter the
thickness of the coat layer of the partition walls can be adjusted
to be a desired value by controlling the particle size, the
compounding ratio, and the like in the framework particles in the
ceramic slurry; the porosity can be adjusted to be a desired value
by controlling the particle size of the framework particles, the
amount of the pore former, and the like in the ceramic slurry; and
the thickness of the coat layer of the partition walls can be
adjusted to be a desired value by controlling concentration of the
ceramic slurry, time required for the membrane formation, and the
like.
Incidentally, since the catalyst component such as an oxidation
catalyst and a NOx adsorber catalyst is loaded in a highly
dispersed state, it is preferable to load the catalyst component on
the partition walls and the like of the honeycomb-structured body
after once loading it on a thermal resistant inorganic oxide having
a large specific surface area such as alumina in advance.
In addition, the aforementioned PM removal catalyst can be loaded
by, for example, a method where catalyst slurry is loaded inside
the pores of the partition walls by applying a conventionally known
catalyst-loading method such as dipping or suction, followed by
drying and firing.
An example of the production method of a honeycomb-structured body
is the following method. However, without limiting to the
production method of a honeycomb-structured body, a known
production method of a honeycomb-structured body can be
employed.
In a case that a honeycomb-structured body is a honeycomb segment
bonded body 63 composed of plural honeycomb segments 62 as shown in
FIG. 13 and formed by bonding the segments with a bonding material
64 and subjecting the outer peripheral surface to cutting to have a
desired shape, the method may be performed in the following
procedure.
In the first place, honeycomb segments are produced. As the
honeycomb segment raw material, for example, a SiC powder and a
metal Si powder are mixed at a mass ratio of 80:20, and methyl
cellulose, hydroxypropoxymethyl cellulose, a surfactant, and water
are added to the mixture, and they are kneaded to obtain kneaded
clay having plasticity. Then, the kneaded clay is subjected to
extrusion forming using a predetermined die to obtain honeycomb
segment formed bodies having a desired shape. Next, after the
resultant honeycomb segment formed articles are dried with a
microwave drier and further completely dried with a hot air drier,
plugging is performed, followed by firing (calcination).
The calcination is performed for degreasing. The degreasing is
performed, for example, at 550.degree. C. for about three hours in
an oxidation atmosphere. However, the conditions are not limited to
these conditions, and it is preferable that the conditions are
according to the organic matter (organic binder, dispersant, pore
former, etc.) in the honeycomb formed body. Generally, since the
combustion temperature of the organic binder is about 100 to
300.degree. C., and the combustion temperature of the pore former
is about 200 to 800.degree. C., the calcination temperature is
about 200 to 1000.degree. C. Though there is no particular
limitation on the calcination time, it is generally about 3 to 100
hours.
Further, the firing (main firing) is performed the "main firing"
means an operation for securing predetermined strength by sintering
the forming raw material in a calcined body for densification.
Since the firing conditions (temperature and time) are different
depending on the kind of the raw material, appropriate conditions
may be selected in accordance with the kind. For example, a firing
temperature in the case of firing in an Ar inert atmosphere is
generally about 1400 to 1500.degree. C. However, the temperature is
not limited to the above range.
After the plural honeycomb segments (sintered bodies) having a
desired size are obtained through the aforementioned steps, bonding
slurry obtained by kneading aluminosilicate fiber, colloidal
silica, polyvinyl alcohol, and silicon carbide is applied on the
peripheral faces of the honeycomb segments, and the honeycomb
segments are combined and press-fitted, followed by heating-drying
to obtain a honeycomb segment bonded body having a quadrangular
columnar entire shape. Then, after the honeycomb segment bonded
body is cut to have a circular columnar shape, the peripheral faces
are covered with an outer periphery coat layer of the same material
as that for the honeycomb segment formed body, followed by drying
and hardening to obtain a circular columnar honeycomb-structured
body having a segment structure.
As a method for forming plugging portions, plugging slurry is
stored in a storage container. Then, an end portion having the
aforementioned mask applied thereto is immersed in the slurry in
the storage container to fill the plugging slurry into the opening
portions of the cells having no mask, thereby forming plugging
portions. A mask is applied to the other end portions of the cells
plugged in the one end portions, and plugging portions are formed
in the same manner as in the formation of plugging portions on the
aforementioned one end portions. Thus, the other end portions of
the cells which are not plugged in the aforementioned one side end
portions are plugged to have a structure where the cells are
alternately plugged in the checkerwise pattern on the other end
portions. In addition, the plugging may be performed after the
honeycomb fired body is formed by firing the honeycomb formed
body.
Incidentally, when the same material as the honeycomb segment raw
material is used as the plugging material, the expansion
coefficient upon firing can be made the same as that of the
honeycomb segments to improve durability, which is preferable.
Incidentally, as a forming method, a method where kneaded clay
prepared as described above is subjected to extrusion forming using
a die having a desired cell shape, partition wall thickness, and
cell density can suitably be employed.
Incidentally, a honeycomb filter of the present invention can
suitably be used as a diesel particulate filter (DPF) for trapping
particulate matter (PM) discharged from a diesel engine.
[2-1] First Production Method of the Present Invention:
As an embodiment of the first production method of a honeycomb
filter of the present invention, it is preferable that the method
includes the steps of: forming a honeycomb formed body by
subjecting a forming raw material containing a ceramic raw material
to extrusion forming and forming plugging portions in one side open
end portions and the other side open end portions of the other
cells of the honeycomb formed body, firing the honeycomb formed
body to form a honeycomb fired body, supplying particles having an
average particle diameter smaller than that of the particles
constituting the partition walls from the one side open end
portions of the honeycomb fired body by a solid-gas two-phase flow,
and, at least in open pores formed by the particles constituting
the partition wall and/or gaps between the particles, forming a
composite region by depositing particles having an average particle
diameter smaller than that of the aforementioned particles in a
surface layer portion of the partition walls on the exhaust gas
inflow side; wherein the partition walls have an average pore
diameter of 5 to 40 .mu.m and a porosity of 35 to 75%, the
particles deposited has an average particle diameter of 1 to 15
.mu.m, and the composite region has a height of 80 .mu.m or less
with respect to the partition wall surface direction from the
outermost contour line of the partition walls. By such production,
the contact area between the deposited particles is decreased, and
securing of the gaps between the particles, that is, passages
becomes easy, and pressure loss can be suppressed.
Specifically, in the first place, as described above, the forming
raw material containing a ceramic raw material is subjected to
extrusion forming to form a honeycomb formed body provided with
partition walls separating and forming plural cells functioning as
fluid passages and extending over from one side end face to the
other side end face. Next, a honeycomb-structured body where
plugging portions are formed in one side open end portions and the
other side open end portions of the other cells of the honeycomb
formed body is prepared.
Further, a honeycomb-structured body was subjected to firing (main
firing) to form a honeycomb fired body. Since the firing conditions
(temperature and time) here are different depending on the kind of
the raw material, suitable conditions may be selected in accordance
with the kind. For example, the firing temperature in the case of
firing in the Ar inert atmosphere is generally about 1400 to
1500.degree. C., and firing time is 1 to 20 hours. However, the
conditions are not limited to these.
Further, from one side open end portions of the aforementioned
honeycomb fired body, particles having the average particle
diameter smaller than that of the particles constituting the
partition walls are supplied by a solid-gas two-phase flow to
deposit the particles having the average particle diameter smaller
than that of the particles constituting the partition walls at
least in open pores formed by the particles constituting the
partition wall and/or gaps between the particles. Thus, a honeycomb
filter having at least the composite region can be obtained.
For example, as a method for depositing the particles having an
average particle diameter smaller than that of the particles
constituting the partition walls by supplying them by a solid-gas
two-phase flow, there is a method where the air containing
particles to be deposited in the open pores formed by the particles
constituting the partition wall and/or the gap between the
particles is sent into the honeycomb filter (DPF) from the exhaust
gas inlet side end face (end face on the exhaust gas inlet side of
the DPF) of the honeycomb filter. Such a method enables to form the
composite region by gradually depositing particles in the open
pores formed in the partition walls of the cells (inlet cells)
where the inlet of the gas is open and/or the gaps between the
particles and on the partition walls. Further, by sucking the
particles from the exhaust gas inlet side end face (exhaust gas
inlet side end face of the DPF) of the honeycomb filter, the
particles are introduced into the partition wall pores to be able
to further stabilize the deposition state.
Incidentally, upon depositing particles in the open pores and/or in
the gap between the particles as necessary, it is preferable to
supply the particles having an average particle diameter smaller
than that of the particles constituting the partition walls by a
solid-gas two-phase flow by setting the open end portion where the
exhaust gas flows in of the honeycomb fired body after the
honeycomb formed body is fired to face downward to form a honeycomb
fired body. This makes deposition of the particles easy on the
surface layer portions of the partition walls on the exhaust gas
inflow side and on the partition wall surface layer portions in a
desired region, thereby making formation easy.
Further, a segment-joined honeycomb segment bonded body where
plural honeycomb fired bodies each having a composite region formed
therein are bonded with a bonding material is formed, and grinding
is performed to obtain a circular shape, an oval shape, a race
track shape, or the like. Further, it is possible to coat the outer
periphery with a coating material.
[2-2] Second Production Method of the Present Invention:
As an embodiment of the second production method of a honeycomb
filter of the present invention, it is also preferable that the
method includes the steps of: forming a honeycomb formed body by
subjecting a forming raw material containing a ceramic raw material
to extrusion forming and forming plugging portions in one side open
end portions and the other side open end portions of the other
cells of the honeycomb formed body, firing the honeycomb formed
body to form a honeycomb fired article, supplying particles having
an average particle diameter smaller than that of the particles
constituting the partition walls from the one side open end
portions of the honeycomb fired article by a solid-gas two-phase
flow, at least in open pores formed by the particles constituting
the partition wall and/or gaps between the particles, forming a
composite region by depositing particles having an average particle
diameter smaller than that of the aforementioned particles in a
surface layer portion of the partition walls on the exhaust gas
inflow side, and further performing a thermal treatment; wherein
the partition walls have an average pore diameter of 5 to 40 .mu.m
and a porosity of 35 to 75%, the particles deposited has an average
particle diameter of 1 to 15 .mu.m, and the composite region has a
height of 80 .mu.m or less with respect to the partition wall
surface direction from the outermost contour line of the partition
walls. That is, it is desirable that, after the step forming a
desired composite region, a thermal treatment step is further
performed to produce a honeycomb filter. By such a thermal
treatment, the particles to be deposited, particle assemblages, the
particle layers, and/or surfaces of the partition walls can be
bonded sufficiently, and durability of the composite region can be
improved.
Incidentally, in the second production method of a honeycomb filter
of the present invention, a series of steps from the step of
extrusion-forming a forming raw material containing a ceramic raw
material to the step of depositing the particles by the solid-gas
two-phase flow on the honeycomb fired body are the same as in the
first production method of a honeycomb filter of the present
invention. Therefore, here, the thermal treatment step after the
particles are deposited will be described, and regarding a series
of the step described above, please refer to the first production
method of a honeycomb filter of the present invention.
A honeycomb filter having a composite region formed in the
aforementioned manner is further subjected to a thermal treatment.
The thermal treatment is performed for bonding the particle
assemblage and/or the particle layers to the particle layers, and
the surfaces of the aforementioned partition walls and is different
from the calcination and the main firing for obtaining a honeycomb
fired body.
Incidentally, as examples of the thermal treatment conditions
(temperature and time), the maximum temperature is 1200 to
1350.degree. C. in an ambient atmosphere, and the time for keeping
the target maximum temperature is 30 to 300 minutes.
Thus, after the aforementioned particle assemblages, and/or the
particle layers, and the surfaces of the aforementioned partition
walls are bonded together, a honeycomb segment-joined type
honeycomb segment bonded body bonded with a bonding material is
formed. Further, it is also possible to perform grinding to obtain
a circular shape, an oval shape, a race track shape, or the like
and to further coat the outer periphery with a coating
material.
Incidentally, after a product is completed, a catalyst coat step is
performed to obtain a honeycomb filter with a catalyst in both the
first production method and the second production method of a
honeycomb filter of the present invention. The catalyst
distribution, composition, and the like of the catalyst used in the
catalyst coat step are as shown in [0098] to [0102], and the
catalyst coat method is as shown in [0103] to [0105].
[2-3] Third Production Method of the Present Invention:
As an embodiment of the third production method of a honeycomb
filter of the present invention, it is also desirable that the
method includes the steps of: forming a honeycomb formed body by
subjecting a forming raw material containing a ceramic raw material
to extrusion forming and forming plugging portions in one side open
end portions and the other side open end portions of the other
cells of the honeycomb formed body, firing the honeycomb formed
body to form a honeycomb fired body, loading a catalyst on the
partition walls of the honeycomb fired body to obtain a
catalyst-loaded honeycomb-structured body, supplying particles
having an average particle diameter smaller than that of the
particles constituting the partition walls from the one side open
end portions of the catalyst-loaded honeycomb-structured body by a
solid-gas two-phase flow, at least in open pores formed by the
particles constituting the partition wall and/or gaps between the
particles, forming a composite region by depositing particles
having an average particle diameter smaller than that of the
aforementioned particles in a surface layer portion of the
partition walls on the exhaust gas inflow side, and further
performing a thermal treatment; wherein the partition walls have an
average pore diameter of 5 to 40 .mu.m and a porosity of 35 to 75%,
the particles deposited have an average particle diameter of 1 to
15 .mu.m, and the composite region has a height of 80 .mu.m or less
with respect to the partition wall surface direction from the
outermost contour line of the partition walls. Thus, since the
composite region is formed after the catalyst is coated, there is
no substantial deposition of a catalyst in the composite region.
Therefore, the clogging of the gaps (spaces) between the particles
in the composite region is not caused substantially. As a result,
there is little concern about the rise of the pressure loss
incidence rate of the partition walls. In addition, upon coating
the catalyst, it is not necessary to pay attention to avoiding the
clogging in the composite region with the coating of a catalyst in
the composite region. Therefore, the restriction of the catalyst
coat step is small, and catalyst coat can be performed at low
costs.
In the first place, in the third production method of a honeycomb
filter of the present invention, a series of steps from the step of
subjecting a forming raw material containing the ceramic raw
material to extrusion forming to the step of obtaining a honeycomb
fired body are performed in the same manner as in the first
production method of a honeycomb filter of the present invention.
Next, a catalyst is coated on the honeycomb fired body (segments
because they are not yet bonded). Incidentally, the catalyst
distribution, component, and the like of the catalyst used in the
catalyst coating step are as shown in [0098] to [0102], and the
catalyst coating method is as shown in [0103] to [0105].
Further, after the catalyst is coated, the composite region is
formed in the same manner as in the second production method of a
honeycomb filter of the present invention on the honeycomb fired
body with a catalyst coating (with a catalyst). Then, through the
thermal treatment step in the same manner as in the second
production method of a honeycomb filter of the present invention,
the segment-joined type honeycomb segment bonded body bonded with a
bonding material is formed. Further, grinding is performed to
obtain a circular shape, an oval shape, a race track shape, or the
like to further coat the outer periphery with a coating material to
produce a honeycomb filter with a catalyst.
Incidentally, regarding the catalyst coating method in the third
production method of the present invention, the following catalyst
coating method may be employed besides the catalyst coating method
(see [0103] to [0105]) described above. For example, after catalyst
slurry is coated by dipping, suction, or the like, surplus slurry
is blown away by air blow. Then, without the drying step, particles
are deposited in a wet state after the air blow unlike the
conventional method where the drying step follows. Then, a thermal
treatment step including both a catalyst-drying step and a thermal
treatment step for forming the composite region is performed. By
employing such a catalyst coating method, the treatment steps in
catalyst coat can be reduced to be able to plan the reduction in
costs. Incidentally, as the thermal treatment conditions in a
thermal treatment step including both a catalyst-drying step and a
thermal treatment step for forming the composite region, the
maximum temperature is 450 to 750.degree. C. in an ambient
atmosphere, and the time for keeping the target maximum temperature
is 30 to 180 minutes.
Further, it is also preferable that, in addition to the third
production method of a honeycomb filter of the present invention,
the method includes the steps of: supplying particles having an
average particle diameter smaller than that of the particles
constituting the partition walls from one side open end portion of
the honeycomb fired body by a solid-gas two-phase flow, and
simultaneously, sucking the particles from the other open end
portions of the honeycomb fired body to deposit the particles in
the pores formed in the partition walls on the exhaust gas inflow
side to form a composite region. By thus sucking the particles from
the downstream side (the other open end portion side of the
honeycomb fired body) simultaneously with sending the carrier air
carrying the particles, particles can stably be deposited on the
honeycomb fired body in a short period of time.
EXAMPLE
Hereinbelow, the present invention will be described more
specifically by Examples. However, the present invention is by no
means limited to these Examples. Incidentally, "part" and "%" in
the following Examples and Comparative Examples mean mass part and
mass % unless otherwise noted. In addition, the various evaluations
and measurements in Examples were carried out by the following
methods.
[1] Full Load Pressure Loss:
In order to evaluate the pressure loss in the state of no soot
deposition, a DPF was mounted on a 2.2 L engine, and, after the
engine warm up for five minutes, a full load state at 4000 rpm was
kept for five minutes to measure the pressure loss on the front and
back of the honeycomb filter (DPF) at that time.
[2] Pressure Loss with Soot
In order to evaluate the pressure loss at the time of soot
deposition, a DPF is mounted on the same engine, and, with
constantly depositing soot with 200 rpm.times.50 Nm, the behavior
of the pressure loss rise was measured. After the test, the weight
was measured to confirm the deposited soot amount.
[3] Trapping Efficiency:
Upon measuring the pressure loss with soot of [2], the soot amount
on the front and back of the DPF (gas inlet side and gas outlet
side of the DPF) right after the DPF was mounted on the engine was
measured with the SMPS (Scanning Mobility Particle Sizer produced
by TSI Incorporated) to calculate the trapping efficiency of the
DPF.
[4] Isostatic Strength Test:
The DPF was covered with a rubber cover lest water should enter the
inside of the DPF, and hydrostatic pressure was applied to the DPF
in water to measure the pressure where the DPF was destroyed.
Example 1
A SiC powder and a metal Si powder were mixed together at the mass
ratio of 80:20; methyl cellulose, hydroxypropoxylmethyl cellulose,
a surfactant, and water were added to the mixture, followed by
kneading to obtain kneaded clay having plasticity; and the kneaded
clay was subjected to extrusion forming using a predetermined die
to obtain a total of 16 (4.times.4) honeycomb segments having a
desired shape. Next, after the honeycomb segment formed bodies
obtained above were dried with a microwave drier and further dried
completely with a hot air drier, plugging was performed, and firing
(calcination) was performed. The condition of the calcination was
550.degree. C. for three hours in an oxidation atmosphere. Then,
firing (main firing) was performed. The firing conditions
(temperature and time) were 1400.degree. C. for two hours in an Ar
inert atmosphere.
From the open end portions on the exhaust gas inflow side of the
honeycomb segments obtained above, SiC particles having an average
particle diameter of 3 .mu.m were supplied by a solid-gas two-phase
flow to deposit the SiC particles having an average particle
diameter of 3 .mu.m in the open pores formed by the particles
constituting the partition walls and/or the gap between the
particles in the surface layer portion of the partition walls on
the exhaust gas inlet side to form a composite region. Next, a
thermal treatment was performed at the maximum temperature of
1300.degree. C. with the maximum temperature keeping time of two
hours to bond the SiC particles together and bond the SiC particles
and the partition walls. Thus, there were obtained honeycomb
segments (composite region-formed bodies) having a rib thickness
(partition wall thickness) of 300 .mu.m, a cell pitch of 1.47 mm, a
porosity of 40%, an average pore diameter of 15 .mu.m, and an
average particle diameter (particles constituting the partition
walls) of 50 .mu.m as partition wall properties and an average
particle diameter of 3 .mu.m, a composite region depth (composite
region thickness in the partition wall thickness direction) of 10
.mu.m, a composite region depth rate (rate of the composite region
depth with respect to the partition wall thickness) of 3.3%, and a
distance from the outermost contour line of 20 .mu.m as the
composite region/layer properties. On the peripheral face of each
of the honeycomb segments obtained above was applied bonding slurry
obtained by kneading aluminosilicate fibers, colloidal silica,
polyvinyl alcohol, and silicon carbide, and the segments were
combined and press-fitted, followed by heating-drying to obtain a
honeycomb segment bonded body having an entire quadrangular
columnar shape. Further, after the honeycomb segment bonded body
was ground into a circular columnar shape, the peripheral face was
covered with an outer periphery coat layer formed of the same
material as the bonding slurry, followed by drying for hardening to
obtain a circular columnar honeycomb-structured body having a
segment structure having a diameter of 144 mm, a length of 152 mm,
a partition wall thickness of 300 .mu.m, and a cell density of 46.5
cells/cm.sup.2.
Next, a catalyst was loaded on the partition walls of the
honeycomb-structured body obtained above. In the first place, there
was previously prepared slurry of a catalyst containing alumina,
platinum, and ceria based material at a proportion of 7:1:2 (mass
ratio) with the ceria based material containing Ce, Zr, Pr, Y, and
Mn at a proportion of 60:20:10:5:5 (mass ratio). Next, the
honeycomb-structured body was immersed up to a predetermined height
from the outlet end face (exhaust gas outflow side end face), and
suction is performed for a predetermined period of time with
adjusting the suction pressure and the suction flow rate to have
predetermined suction pressure and suction flow rate to load a
catalyst on the partition walls, followed by drying at 120.degree.
C. for two hours and baking at 550.degree. C. for one hour to
obtain a catalyst-loaded honeycomb filter of Example 1. The
aforementioned experiments [1] to [3] were performed. The partition
wall properties, composite region/layer properties, and the
experiment results are shown in Table 1.
TABLE-US-00001 TABLE 1 Composite region/layer property Partition
wall property Distance Aver- Com- from Average age Com- posite
outer- Evaluation result Rib pore particle Average posite region
most Full load Pressure Trapping thick- Cell Poros- diam- diam-
Particle region depth contour pressure los- s with effi- Isostatic
ness pitch ity eter eter diameter depth rate line loss soot ciency
streng- th No. [.mu.m] [mm] [%] [.mu.m] [.mu.m] [.mu.m] [.mu.m] [%]
[.mu.m] [kPa] [kP- a] [%] [MPa] Comp. Ex. 1 300 1.47 40 15 50 3 0 0
50 32 17 82 -- Comp. Ex. 2 300 1.47 40 15 50 3 0 0 20 26 16 69 --
Comp. Ex. 3 300 1.47 40 15 50 -- 0 0 0 18 18 61 -- Example 1 300
1.47 40 15 50 3 10 3.3 20 16 9 85 -- Example 2 300 1.47 40 15 50 3
20 6.7 20 16 9 88 -- Example 3 300 1.47 40 15 50 3 50 16.7 20 16 9
89 -- Example 4 300 1.47 40 15 50 3 80 26.7 20 16 9 88 -- Example 5
300 1.47 40 15 50 3 90 30.0 20 16 10 89 -- Example 6 300 1.47 40 15
50 3 100 33.3 20 18 18 89 -- Comp. Ex. 4 300 1.47 40 15 50 0.5 20
6.7 20 26 19 89 -- Comp. Ex. 5 300 1.47 40 15 50 0.8 20 6.7 20 24
17 89 -- Example 7 300 1.47 40 15 50 1 20 6.7 20 17 9 88 -- Example
8 300 1.47 40 15 50 5 20 6.7 20 16 9 87 -- Example 9 300 1.47 40 15
50 15 20 6.7 20 16 9 83 -- Comp. Ex. 6 300 1.47 40 15 50 18 20 6.7
20 16 9 68 -- Comp. Ex. 7 300 1.47 40 15 50 3 20 6.7 82 28 16 89 --
Example 10 300 1.47 40 15 50 3 20 6.7 80 19 9 88 -- Example 11 300
1.47 40 15 50 3 20 6.7 70 17 9 88 -- Example 12 300 1.47 40 15 50 3
20 6.7 50 18 9 89 -- Example 13 300 1.47 40 15 50 3 20 6.7 30 18 10
88 -- Example 14 300 1.47 40 15 50 3 20 6.7 10 16 9 89 -- Example
15 300 1.47 40 15 50 3 20 6.7 5 16 9 89 --
Example 2 to 6
There were obtained honeycomb segments (composite region-formed
bodies) provided with the same partition wall properties as in
Example 1 and different from Example 1 in that the composite region
depth (thickness of the composite region in the partition wall
thickness) was 20 .mu.m and that the composite region depth rate
(rate of the composite region depth with respect to the partition
wall thickness) was 6.7%. Further, through the same steps as in
Example 1, honeycomb segment bonded articles were obtained. After
the honeycomb segment bonded articles were subjected to grinding
into a circular columnar shape, the peripheral face was coated with
an outer periphery coat layer of a material equivalent to the
bonding slurry, followed by drying for hardening to obtain a
circular columnar honeycomb-structured body having a segment
structure having a diameter of 144 mm, a length of 152 mm, a
partition wall thickness of 300 .mu.m, and a cell density of 46.5
cells/cm.sup.2. A catalyst was loaded on the honeycomb-structured
body obtained above in the same manner as in Example 1 to obtain a
honeycomb filter of Example 2. Incidentally, since Examples 3 to 24
employ a circular columnar honeycomb filter having a segment
structure having a diameter of 144 mm, a length of 152 mm, a
partition wall thickness of 300 .mu.m, and a cell density of 46.5
cells/cm.sup.2, the description will be omitted. In the same
manner, in Example 3, after the honeycomb segments (composite
region-formed bodies) were obtained in the same manner as in
Example 1 except that the composite region depth (thickness of the
composite region in the direction of partition wall thickness) was
50 .mu.m and that the composite region depth rate (composite region
depth rate with respect to the thickness of the partition wall) was
16.7% as the composite region/layer properties, a honeycomb filter
was obtained through the same steps as in Example 1. In the same
manner, in Example 4, after honeycomb segments (composite
region-formed bodies) were obtained in the same manner as in
Example 1 except that the composite region depth (thickness of the
composite region in the direction of partition wall thickness) was
80 .mu.m and that the composite region depth rate (composite region
depth rate with respect to the thickness of the partition wall) was
26.7% as the composite region/layer properties, a honeycomb filter
was obtained through the same steps as in Example 1. In the same
manner, in Example 5, after honeycomb segments (composite
region-formed bodies) were obtained in the same manner as in
Example 1 except that the composite region depth (thickness of the
composite region in the direction of partition wall thickness) was
90 .mu.m and that the composite region depth rate (composite region
depth rate with respect to the thickness of the partition wall) was
30.0% as the composite region/layer properties, a honeycomb filter
was obtained through the same steps as in Example 1. In the same
manner, in Example 6, after honeycomb segments (composite
region-formed bodies) were obtained in the same manner as in
Example 1 except that the composite region depth (thickness of the
composite region in the direction of partition wall thickness) was
100 .mu.m and that the composite region depth rate (composite
region depth rate with respect to the thickness of the partition
wall) was 33.3% as the composite region/layer properties, a
honeycomb filter was obtained through the same steps as in Example
1. This was used as Example 6. The thus obtained catalyst-loaded
honeycomb filters of Examples 2 to 6 were subjected to the
aforementioned experiments [1] to [3]. The results of the
experiments, partition wall properties, and composite region/layer
properties are shown in Table 1.
Examples 7 to 9
In addition, after honeycomb segments (composite region-formed
bodies) which were the same as those of Example 2 except that the
average particle diameter was 1 .mu.m as a composite region/layer
property were obtained, a honeycomb filter was obtained through the
same steps as in Example 1. This was employed as Example 7. In
addition, after honeycomb segments (composite region-formed
articles) which were the same as those of Example 2 except that the
average particle diameter was 5 .mu.m as a composite region/layer
property were obtained, a honeycomb filter was obtained through the
same steps as in Example 1. This was employed as Example 8. In
addition, honeycomb segments (composite region-formed bodies) which
were the same as those of Example 2 except that the average
particle diameter was 15 .mu.m as a composite region/layer property
were obtained, a honeycomb filter was obtained through the same
steps as in Example 1. This was employed as Example 9. The thus
obtained catalyst-loaded honeycomb filters of Examples 7 to 9 were
subjected to the aforementioned experiments [1] to [3]. The results
of the experiments, partition wall properties, and composite
region/layer properties are shown in Table 1.
Examples 10 to 15
In addition, after honeycomb segments (composite region-formed
bodies) which were the same as those of Example 2 except that the
distance from the outermost contour line was 80 .mu.m as a
composite region/layer property were obtained, a honeycomb filter
was obtained through the same steps as in Example 1. This was
employed as Example 10. In addition, after honeycomb segments
(composite region-formed articles) which were the same as those of
Example 2 except that the distance from the outermost contour line
was 70 .mu.m as a composite region/layer property were obtained, a
honeycomb filter was obtained through the same steps as in Example
1. This was employed as Example 11. In addition, after honeycomb
segments (composite region-formed bodies) which were the same as
those of Example 2 except that the distance from the outermost
contour line was 50 .mu.m as a composite region/layer property were
obtained, a honeycomb filter was obtained through the same steps as
in Example 1. This was employed as Example 12. In addition, after
honeycomb segments (composite region-formed bodies) which were the
same as those of Example 2 except that the distance from the
outermost contour line was 30 .mu.m as a composite region/layer
property were obtained, a honeycomb filter was obtained through the
same steps as in Example 1. This was employed as Example 13. In
addition, after honeycomb segments (composite region-formed bodies)
which were the same as those of Example 2 except that the distance
from the outermost contour line was 10 .mu.m as a composite
region/layer property were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This was employed
as Example 14. In addition, after honeycomb segments (composite
region-formed bodies) which were the same as those of Example 2
except that the distance from the outermost contour line was 5
.mu.m as a composite region/layer property were obtained, a
honeycomb filter was obtained through the same steps as in Example
1. This was employed as Example 15. The thus obtained
catalyst-loaded honeycomb filters of Examples 10 to 15 were
subjected to the aforementioned experiments [1] to [3]. The results
of the experiments, partition wall properties, and composite
region/layer properties are shown in Table 1.
Examples 16 to 19
In addition, after honeycomb segments (composite region-formed
bodies) which were the same as those of Example 2 except that the
porosity was 35% and that the average particle diameter was 45
.mu.m as partition wall properties were obtained with adjusting the
particle diameter distribution (sharp, broad, two peak
distribution, etc.) and the pore former (particle diameter,
particle diameter distribution, and addition amount), a honeycomb
filter was obtained through the same steps as in Example 1. This
was employed as Example 16. In the same manner, after honeycomb
segments (composite region-formed articles) which were the same as
those of Example 2 except that the porosity was 50% and that the
average particle diameter was 40 .mu.m as partition wall properties
were obtained, a honeycomb filter was obtained through the same
steps as in Example 1. This was employed as Example 17. In the same
manner, after honeycomb segments (composite region-formed bodies)
which were the same as those of Example 2 except that the porosity
was 60% and that the average particle diameter was 35 .mu.m as
partition wall properties were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This was employed
as Example 18. In the same manner, after honeycomb segments
(composite region-formed bodies) which were the same as those of
Example 2 except that the porosity was 75% and that the average
particle diameter was 25 .mu.m as partition wall properties were
obtained, a honeycomb filter was obtained through the same steps as
in Example 1. This was employed as Example 19. The thus obtained
honeycomb filters with a catalyst of Examples 16 to 19 were
subjected to the aforementioned experiments [1] to [4]. The results
of the experiments, partition wall properties, and composite
region/layer properties are shown in Table 2.
Examples 20 to 24
In addition, after honeycomb segments (composite region-formed
bodies) which were the same as those of Example 2 except that the
average pore diameter was 5 .mu.m and that the average particle
diameter was 10 .mu.m as partition wall properties were obtained, a
honeycomb filter was obtained through the same steps as in Example
1. This was employed as Example 20. In addition, after honeycomb
segments (composite region-formed bodies) which were the same as
those of Example 2 except that the average pore diameter was 10
.mu.m and that the average particle diameter was 35 .mu.m as
partition wall properties were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This was employed
as Example 21. In addition, after honeycomb segments (composite
region-formed bodies) which were the same as those of Example 2
except that the average pore diameter was 30 .mu.m as a partition
wall property were obtained, a honeycomb filter was obtained
through the same steps as in Example 1. This was employed as
Example 22. In addition, after honeycomb segments (composite
region-formed bodies) which were the same as those of Example 2
except that the average pore diameter was 35 .mu.m and that the
average particle diameter was 60 .mu.m as partition wall properties
were obtained, a honeycomb filter was obtained through the same
steps as in Example 1. This was employed as Example 23. In
addition, after honeycomb segments (composite region-formed bodies)
which were the same as those of Example 2 except that the average
pore diameter was 40 .mu.m and that the average particle diameter
was 65 .mu.m as partition wall properties were obtained, a
honeycomb filter was obtained through the same steps as in Example
1. This was employed as Example 24. The thus obtained honeycomb
filters with a catalyst of Examples 20 to 24 were subjected to the
aforementioned experiments [1] to [3]. The results of the
experiments, partition wall properties, and composite region/layer
properties are shown in Table 2.
TABLE-US-00002 TABLE 2 Composite region/layer property Partition
wall property Distance Aver- Com- from Average age Com- posite
outer- Evaluation result Rib pore particle Average posite region
most Full load Pressure Trapping thick- Cell Poros- diam- diam-
Particle region depth contour pressure los- s with effi- Isostatic
ness pitch ity eter eter diameter depth rate line loss soot ciency
streng- th No. [.mu.m] [mm] [%] [.mu.m] [.mu.m] [.mu.m] [.mu.m] [%]
[.mu.m] [kPa] [kP- a] [%] [MPa] Comp. Ex. 8 300 1.47 33 15 50 3 20
6.7 20 34 18 89 4.2 Example 16 300 1.47 35 15 45 3 20 6.7 20 17 10
89 4 Example 17 300 1.47 50 15 40 3 20 6.7 20 16 9 88 3.3 Example
18 300 1.47 60 15 35 3 20 6.7 20 16 9 89 2.8 Example 19 300 1.47 75
15 25 3 20 6.7 20 16 9 89 1.4 Comp. Ex. 9 300 1.47 78 15 20 3 20
6.7 20 16 9 88 0.8 Comp. Ex. 10 300 1.47 40 4 10 3 20 6.7 20 36 17
92 -- Example 20 300 1.47 40 5 10 3 20 6.7 20 18 10 89 -- Example
21 300 1.47 40 10 35 3 20 6.7 20 17 9 89 -- Example 22 300 1.47 40
30 50 3 20 6.7 20 16 9 88 -- Example 23 300 1.47 40 35 60 3 20 6.7
20 16 9 88 -- Example 24 300 1.47 40 40 65 3 20 6.7 20 16 9 85 --
Comp. Ex. 11 300 1.47 40 43 65 3 20 6.7 20 19 9 68 --
Comparative Example 1 to 3
There were obtained honeycomb segment bonded body having an entire
quadrangular columnar shape by applying bonding slurry obtained by
kneading aluminosilicate fibers, colloidal silica, polyvinyl
alcohol, and silicon carbide on the peripheral faces of the
honeycomb segments as it is without supplying p bodies in the
composite region after the honeycomb segments were obtained in the
same manner as in Example 1, joining the honeycomb segments and
press-fitting them, followed by heating-drying. Further, after
grinding the honeycomb segment bonded body into a circular columnar
shape, the peripheral face was coated with the outer periphery coat
layer formed of a material equivalent to the bonding slurry,
followed by drying for hardening to obtain a circular columnar
honeycomb filter having a segment structure having a diameter of
144 mm, a length of 152 mm, a partition wall thickness of 300
.mu.m, and a cell density of 46.5 cells/cm.sup.2. Incidentally,
since Comparative Examples 2 to 11 employ a circular columnar
honeycomb filter having a segment structure having a diameter of
144 mm, a length of 152 mm, a partition wall thickness of 300
.mu.m, and a cell density of 46.5 cells/cm.sup.2, the description
will be omitted. Further, in the same manner as in Example 1,
catalyst coating was performed to obtain a catalyst-loaded
honeycomb filter. The catalyst-loaded honeycomb filter had a rib
thickness (partition wall thickness) of 300 .mu.m, a cell pitch of
1.47 mm, a porosity of 40%, an average pore diameter of 15 .mu.m,
and an average particle diameter (of particles constituting the
partition walls) of 50 .mu.m as partition wall properties and an
average particle diameter of 3 .mu.m, a composite region depth
(thickness of the composite region in the direction of partition
wall thickness) of 0 .mu.m, a composite region depth rate (the rate
of the composite region depth with respect to the partition wall
thickness) of 0%, and a distance from the outermost contour line of
50 .mu.m as composite region/layer properties, and it was employed
as Comparative Example 1. In the same manner, a catalyst-loaded
honeycomb filter which was the same as that of Comparative Example
1 except that the distance from the outermost contour line was 20
.mu.m was employed as Comparative Example 2. In the same manner, a
catalyst-loaded honeycomb filter which was the same as that of
Comparative Example 1 except that the distance from the outermost
contour line was 0 .mu.m with "-" for the "average particle
diameter" was employed as Comparative Example 3. Thus, the
Comparative Examples 1 to 3 were subjected to the aforementioned
experiments [1] to [3]. The results are shown in Table 1.
Incidentally, in Comparative Examples 1 to 3 shown in Table 1, that
the "composite region depth" was "0" in the "composite region/layer
properties" means that there was no particle deposition in the
composite region on the downstream side of the surface layer
reference line and that particles were deposited only above the
surface layer reference line (on the partition wall surface layer
side on the upstream side of the surface layer reference line
(partition wall surface side on the upstream side of the surface
layer reference line)). In the same manner, the "average particle
diameter" in the "composite region/layer properties" of Comparative
Examples 1 and 2 shows the particle diameter of the particle
assemblages present on the upstream side of the surface layer
reference line (on the partition wall surface layer side on the
upstream side of the surface layer reference line (partition wall
surface side on the upstream side of the surface layer reference
line)). Incidentally, the "distance from the outermost contour
line" in the "composite region/layer properties" shows the distance
from the outermost contour line to the particle assemblages present
on the upstream side of the surface layer reference line (on the
partition wall surface layer side on the upstream side of the
surface layer reference line (partition wall surface side on the
upstream side of the surface layer reference line)). In addition,
that the "average particle diameter" in the "composite region/layer
properties" of Comparative Example 3 is "-" means that both the
"composite region depth" and the "distance from the outermost
contour line" were zero, i.e., conventional partition walls where
no particle deposits.
Comparative Example 4 to 7
In the same manner, after the honeycomb segments (composite
region-formed bodies) which were the same as those in Example 2
except for the average particle diameter of 0.5 .mu.m as a
composite region/layer property were obtained, a honeycomb filter
was obtained through the same steps as in Example 1. This filter
was employed as Comparative Example 4. In the same manner, after
the honeycomb segments (composite region-formed articles) which
were the same as those in Example 2 except for the average particle
diameter of 0.8 .mu.m as a composite region/layer property were
obtained, a honeycomb filter was obtained through the same steps as
in Example 1. This filter was determined as Comparative Example 5.
In the same manner, after the honeycomb segments (composite
region-formed bodies) which were the same as those in Example 2
except for the average particle diameter of 18 .mu.m as a composite
region/layer property were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This filter was
employed as Comparative Example 6. In the same manner, after the
honeycomb segments (composite region-formed articles) which were
the same as those in Example 2 except for the distance from the
outermost contour of 82 .mu.m as a composite region/layer property
were obtained, a honeycomb filter was obtained through the same
steps as in Example 1. The filter was employed as Comparative
Example 7. Thus, the Comparative Examples 4 to 7 were subjected to
the aforementioned experiments [1] to [3]. The results are shown in
Table 1.
Comparative Example 8 to 11
In addition, after the honeycomb segments (composite region-formed
bodies) which were the same as those in Example 2 except for the
porosity of 33% as a partition wall property were obtained with
adjusting the particle diameter distribution (sharp, broad, two
distribution) and adjusting the pore former (particle diameter,
particle diameter distribution, addition amount), a honeycomb
filter was obtained through the same steps as in Example 1. The
filter was determined as Comparative Example 8. In the same manner,
after the honeycomb segments (composite region-formed bodies) which
were the same as those of Example 2 except that the porosity was
78% and that the average particle diameter was 20 .mu.m as
partition wall properties were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This was employed
as Comparative Example 9. In the same manner, after the honeycomb
segments (composite region-formed bodies) which were the same as
those of Example 2 except that the average pore diameter was 4
.mu.m and that the average particle diameter was 10 .mu.m as
partition wall properties were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This was employed
as Comparative Example 10. In the same manner, after the honeycomb
segments (composite region-formed articles) which were the same as
those of Example 2 except that the average pore diameter was 43
.mu.m and that the average particle diameter was 65 .mu.m as
partition wall properties were obtained, a honeycomb filter was
obtained through the same steps as in Example 1. This was employed
as Comparative Example 11. Thus, Comparative Examples 8 to 11 were
subjected to the aforementioned experiments [1] to [3]. Further,
Comparative Examples 8 and 9 were subjected to the aforementioned
experiment [4]. The results are shown in Table 2.
(Discussion)
As shown in Table 1, good results could be obtained in Examples. On
the other hand, in Comparative Example 3, since the composite
region was not formed in the partition walls, it was confirmed that
pressure loss with soot is high and that the trapping efficiency is
low. In addition, in Comparative Examples 1 and 2, since the rate
of composite region depth was 0, a dense layer of only simulated
ash particles was formed on the partition wall surface layer.
Therefore, the gas permeability remarkably fell, and the rate of
causing the initial pressure loss and pressure loss with soot rose
to a large extent. Incidentally, in Example 6, the composite region
became too large, and, as a result, the rate of clogging partition
wall pores became high. Therefore, the gas permeability became
small, and the pressure loss incidence rate of the partition walls
rose. However, since it was well balanced in comparison with other
Comparative Examples, it is included in Examples in this regard. In
addition, in Comparative Examples 4 and 5, diameter of the
particles forming the composite was too small, and the particles
aggregated and were densified. Therefore, the gap permeability
fell, and the rate of causing the partition wall pressure loss
rose. Further, in Comparative Example 6, the pressure loss
incidence rate of the partition walls rose. Further, in Comparative
Example 6, since the particle diameter was too large, partition
wall open pores could not be clogged efficiently. Therefore,
sufficient trapping efficiency could not be obtained. In addition,
in Comparative Example 7, since the distance of the deposited
particles from the outermost contour is large, the region where the
composite forming particles having small diameters bond to each
other became extremely large. Therefore, the effective volume of
exhaust gas inflow side cells became small, and the line resistance
when exhaust gas passes through the cells rose, and the pressure
loss incidence rate of partition walls rose. In Comparative Example
8, porosity was too low, and the pore passages became small.
Therefore, the gas permeability fell, and the pressure loss
incidence rate of the partition walls rose. In Comparative Example
9, since the porosity was too high, the isostatic strength fell.
When it is 1.0 or less, there is a high possibility that a crack is
caused upon canning. In addition, in Comparative Example 10, since
pores were small, the gas permeability became small, and the
pressure loss incidence rate of the partition walls rose. In
addition, in Comparative Example 11, the pore size was too large to
sufficiently clog the pores even when the composite region was
formed. Therefore, the trapping efficiency was not sufficient.
Thus, in the Comparative Examples, it was confirmed that a defect
was easily caused and that operability was low.
INDUSTRIAL APPLICABILITY
A honeycomb filter of the present invention can suitably be used
for trapping or cleaning up particulates contained in exhaust gas
discharged from an internal combustion engine such as a diesel
engine, an ordinary vehicle engine, and an engine of a large
automobile such as a truck and a bus or various combustion
apparatuses.
DESCRIPTION OF REFERENCE NUMERAL
1, 1A: honeycomb filter, 3: cell, 4: partition wall, 4a: surface
layer portion (composite region), 4b: particles constituting
partition walls, 5: particles (to be deposited), 7: open pore, 9:
gap between particles, ha: open end portion on one side, 11b: open
end portion, 13: plugging portion, 17: outermost contour, 62:
honeycomb segment, 63: honeycomb segment bonded body, 64: bonding
material, 66: outer periphery coat layer, 115: inlet layer, 117:
soot, G, G1, G2: exhaust gas, N: neck portion, R1, R2: particle,
Z1: exhaust gas inflow side, Z2: mid-flow portion (mid-flow
region), Z3: exhaust gas outflow side
* * * * *